Bookkeeping Document Checklist: Every Source Document (2026)

Every bookkeeper has a version of the same list in their head: the statements, reports, invoices and agreements a set of books cannot be built without. The trouble is that it lives in the head, and in a dozen half-finished emails. A new client asks "what do you need from me?" and the answer comes out slightly different every time. Something gets missed, usually the loan agreement or the lease, and it turns up in March when it is too late to be convenient.

This is the master list. It is for independent bookkeepers and small accounting firms in the United States and Canada who want one page that names every source document a client might need to provide, says why each matters and how often it is needed, and then shows how to turn the list into requests that come back. Our monthly bookkeeping checklist covers the monthly close as a set of tasks and a calendar. This guide is about the documents themselves, across the whole life of a client.

What counts as a bookkeeping source document

A source document is the original evidence that a transaction happened and what it was for: the invoice, the receipt, the statement, the signed agreement. Your bookkeeping software holds the record; the source document proves the record is right. When a lender, an auditor, the IRS or the CRA asks a question, the answer is a source document, not a ledger entry.

That is why a bank feed is not a source document. It is a copy of the bank's data with no opening balance, no closing balance and no page numbers. The statement is the source. The same goes for a Shopify deposit: the bank shows the net; the payout report is the source for gross sales, fees and refunds.

The master bookkeeping document checklist

Each table lists the document, why you need it and how often most clients should send it. "Onboarding" means once, when the client joins, or once per new account, loan or asset. "As it happens" means when the event occurs.

1. Bank and credit cards

Document	Why you need it	How often
Bank statements, every business account, every page, as a PDF	The reconciliation anchor: opening and closing balances, every transaction	Monthly
Credit card statements, every business card, every page	Card spending, interest and fees; personal cards used for business count	Monthly
List of every account and card, with the last four digits	So you know which statements to expect	Onboarding, confirm yearly
Statement for the month before your start date	Opening balances tie to something real	Onboarding
Merchant or card processor statements (Stripe, Square, a bank terminal)	Processing fees and the gap between sales and deposits	Monthly
PayPal, Venmo, Wise or other payment account statements	They are bank accounts in all but name	Monthly
Petty cash log	Cash spending that never touches a statement	Monthly
Notice of a new, closed or changed account	A card that appears in month eight means seven months of missing statements	As it happens

Ask for the statement from the bank's website, not a screenshot of the app and not a CSV export. The guides on getting bank statements from clients and read-only bank access for bookkeepers cover the two ways to make this painless.

2. Sales and receivables

Document	Why you need it	How often
Sales invoices issued, or an export from the invoicing system	Revenue, receivables and sales tax collected	Monthly
Payout reports from every sales platform (Shopify, Stripe, Amazon, Etsy, Square, PayPal)	Gross sales, fees, refunds and chargebacks behind each net deposit	Monthly
Point-of-sale sales summary for the month	Total sales, tax and tips for cash and card businesses	Monthly
Customer contracts, quotes and signed proposals for larger jobs	Deposits, progress billing and when revenue is earned	As it happens
Deposit details: which customer and invoice each deposit belongs to	Apply payments correctly and keep receivables clean	Monthly
Customer deposits and gift card balances	Liabilities until earned, not revenue	Monthly or quarterly
Credit notes, refunds and write-offs with the reason	Reverse revenue correctly; support bad debt	As it happens
Accounts receivable aging, if tracked outside your software	Tie open invoices to the books	Month-end or year-end
Sales tax, GST/HST or PST collected by jurisdiction	Sales tax payable and the return	By filing period

3. Purchases and payables

Document	Why you need it	How often
Supplier bills and invoices, paid or unpaid	Expenses, payables and input tax credits	Monthly
Receipts for transactions you cannot categorize from the statement line	Prove what was bought; a card line alone is rarely enough for the IRS or CRA	Monthly
Receipts for any purchase over a threshold you set (for example $75)	Support for larger deductions	Monthly
List of recurring subscriptions and software	Categorize repeat charges once and stop asking	Onboarding, then yearly
Vendor statements at month-end for the main suppliers	Reconcile payables and catch missing bills	Monthly for key vendors
Expense reports from the owner or staff	Business expenses paid personally	Monthly
Mileage log and vehicle expense records	Vehicle deduction and business-use percentage	Monthly or yearly
Home office square footage and household bills	Home office deduction for owners who work from home	Yearly
Accounts payable aging, if tracked outside your software	Tie unpaid bills to the books	Month-end or year-end

For how to get receipts without a monthly argument, see getting clients to send receipts and the missing receipt form template.

4. Payroll and contractors

Document	Why you need it	How often
Payroll register or journal for every pay date	Gross wages, withholdings, deductions, employer taxes and net pay	Monthly
Payroll tax remittance report from the provider	Tie what was withheld to what was paid to the IRS, state or CRA	Monthly
Quarterly payroll filings (Form 941 and state returns in the US; CRA remittance history in Canada)	Reconcile payroll liabilities each quarter	Quarterly
Year-end payroll slips and summaries (W-2 and W-3; T4 and T4 Summary)	Tie the year's wages to the books	Year-end
New hire paperwork: W-4 or TD1, direct deposit form, pay rate	Set the employee up correctly	As it happens
Benefits and workers' compensation invoices	Employer costs and accruals	As billed
Contractor list with total paid in the year	1099-NEC (US) and T4A or T5018 (Canada) preparation	Year-end, updated monthly
W-9 for every US contractor; legal name, address and SIN or business number for Canadian contractors	Required before you can file the slips	Before first payment
Owner draws, distributions or shareholder loan details	Equity, not expense	Monthly

The payroll reports your bookkeeper needs guide names the exact report in Gusto, ADP, QuickBooks Payroll and the Canadian providers. For contractors, see collecting W-9 forms from vendors and the Canadian version on T4A and T5018 contractor information.

5. Loans and leases

Document	Why you need it	How often
Signed loan agreement for every loan and line of credit	Lender, rate, term, security	Onboarding and each new loan
Amortization schedule	Split each payment into principal and interest	Onboarding and each new loan
Closing or funding statement	Fees, holdbacks and the amount actually deposited	Each new loan
Loan and line of credit statements	Balance and interest so the books match the lender	Monthly for lines of credit; at least yearly for term loans
Year-end loan statement with balance and total interest paid	Year-end tie-out and interest expense	Year-end
Equipment and vehicle finance agreements	An asset plus a liability, not a monthly expense	Each new agreement
Premises lease and amendments	Rent, deposits, escalations and lease accounting	Onboarding and renewal
Equipment and vehicle leases	Lease expense or liability, depending on the terms	Onboarding and each new lease
Intercompany and shareholder loan agreements	Related-party tracking	Onboarding
Payoff letters	Close the liability correctly	As it happens

Our guide to loan documents bookkeepers need covers each loan type and what to do with the documents once they arrive.

6. Assets and inventory

Document	Why you need it	How often
Purchase invoice for every piece of equipment, vehicle, computer or furniture over your capitalization threshold	Fixed asset register, depreciation or capital cost allowance	As it happens
Vehicle purchase agreement and registration	Asset cost, business use, financing	Each new vehicle
Bill of sale or trade-in paperwork for assets sold or scrapped	Remove the asset and record the gain or loss	As it happens
Existing fixed asset register or depreciation schedule from the previous accountant	Continue the schedule rather than rebuild it	Onboarding
Inventory count	Cost of goods sold and closing inventory	Year-end, quarterly for larger stock
Inventory purchase invoices and freight bills	Inventory cost	Monthly
Property closing statement, for real estate	Land and building cost	Each purchase
Leasehold improvement invoices	Capitalize and depreciate over the lease	As it happens

If you are picking up a client from another firm, the request records from the previous accountant guide lists what to ask for, including the asset register.

7. Tax

Document	Why you need it	How often
Prior-year business tax return (and the Notice of Assessment in Canada)	Opening balances, elections, carryforwards	Onboarding
Sales tax, GST/HST, PST or QST returns and payment confirmations	Reconcile tax collected and paid to the filings	By filing period
Sales tax registrations and exemption certificates held	Which sales are taxable, and where	Onboarding, then as they change
Estimated tax payment confirmations (Form 1040-ES or corporate estimates in the US; instalments in Canada)	Record payments against the right liability	Quarterly
Every letter or notice from the IRS, a state, the CRA or a province, every page	Penalties, balances, audits and address changes	As it happens
Property tax bills	Expense and, for real estate, cost tracking	Yearly
Business license renewals and local tax filings	Expense and the compliance calendar	Yearly
Tax ID confirmation (EIN letter in the US; business number and program accounts in Canada)	Correct numbers on every filing	Onboarding

A letter from a tax agency is the one document that cannot wait for the monthly request. The guide on what to request when a client gets an IRS or CRA letter lists what to ask for the same day.

8. Legal and entity

Document	Why you need it	How often
Formation documents: articles of incorporation or organization, partnership agreement, or sole proprietor registration	Entity type drives the chart of accounts and the tax return	Onboarding
Operating agreement, bylaws or shareholder agreement	Ownership percentages, distributions, who can sign	Onboarding and amendments
Ownership and officer list	Equity accounts and related parties	Onboarding, confirm yearly
Board or shareholder minutes and resolutions	Dividends, shareholder loans, major purchases	Yearly, or as they happen
Business insurance policies and declarations pages	Prepaid insurance, coverage dates, premium financing	Onboarding and renewal
Signed engagement letter with your firm	The scope you agreed to, including who provides what and by when	Onboarding and renewal
Authorization forms (IRS Form 8821 or 2848; CRA business authorization)	Permission to deal with the agency on the client's behalf	Onboarding
Major contracts: franchise, licensing, distribution	Recurring fees, royalties, deferred revenue	Onboarding and as signed
Correspondence about lawsuits, claims or settlements	Contingent liabilities and legal expense	As it happens

The client onboarding checklist for accounting firms walks through the onboarding items as a sequence, from engagement letter to kickoff. For the scope conversation itself, see the bookkeeping engagement letter template.

Industry add-ons the master list does not cover

Each industry has source documents of its own. Rather than repeat them here, these guides carry the full lists with the exact report names.

Industry	Extra documents on top of the master list	Full checklist
Restaurants and bars	POS sales summary with tax and tips split out, delivery platform payouts, food and beverage vendor statements, tip reports, gift card liability, liquor inventory	Restaurant bookkeeping documents checklist
Construction and trades	Signed contracts, change orders, pay applications, subcontractor invoices, lien waivers, retainage, job-costed receipts, certificates of insurance	Construction bookkeeping documents checklist
Nonprofits, churches and charities	IRS determination letter or CRA registration, grant agreements, donor restrictions, deposit splits by source, in-kind gift details, Form 990 or T3010 items	Nonprofit bookkeeping documents checklist
Self-employed and sole proprietors	Full income record (not just 1099s or T4As), home office measurements, mileage log, health insurance and retirement contributions, tax payments made	Self-employed tax documents checklist
Online sellers	One payout report per platform, sales and sales tax summary per month, settlement statements, marketplace fee reports	Shopify, Stripe and Amazon reports your bookkeeper needs
Rental property owners	Rent roll, mortgage interest statement (Form 1098 in the US), property tax, insurance, repair invoices, management statements, closing statements and improvement invoices	Rental property tax documents checklist

Two situations cut across every industry. A client who is months or years behind needs the documents in a particular order, covered in the catch-up bookkeeping checklist. A client heading into an audit or review needs the PBC list template, which is the master list reorganized the way an auditor asks for it.

Onboarding, monthly and year-end: three standing requests

Nobody should receive the master list as a single email. Split it into three requests that repeat the same way for every client. The master list says which bucket each document belongs in; these tables are the three buckets.

The onboarding request

Sent once, as soon as the engagement letter is signed, with a needed-by date two to three weeks out.

Section	Documents
Entity	Formation documents, operating agreement or bylaws, ownership list, EIN letter or business number, authorization forms
Accounts	List of every bank, card, loan and payment account; statement for the month before the start date; read-only or accountant access invitations
History	Prior-year return and Notice of Assessment, last trial balance or financials, fixed asset register, open invoices and unpaid bills at the start date
Agreements	Every loan agreement with amortization schedule, premises lease, equipment leases and finance agreements, insurance policies, major contracts
People	Payroll provider access, employee list, contractor list with W-9s or Canadian details
Systems	Sales platforms and POS in use, invoicing tool, receipt capture tool, and who at the client sends what

The monthly request

Sent on the same day every month with a needed-by date about a week out. The calendar and email templates are in the monthly bookkeeping checklist.

Section	Documents
Statements	Bank, credit card, line of credit, payment account and processor statements, every page, PDF
Sales	Invoices issued or export, payout reports per platform, POS summary, deposit details
Purchases	Supplier bills, receipts for uncategorized and over-threshold transactions, vendor statements for key suppliers, expense reports
Payroll	Payroll register per pay date, tax remittance report, new hire paperwork, contractor payments
Tax	Sales tax or GST/HST filing and payment for the period, any agency letter received
Questions	Anything unusual: new accounts, loans, large purchases, asset sales, owner draws, refunds

The year-end request

Sent in two parts, before and after the fiscal year-end. The timing and templates are in year-end bookkeeping: what to request from clients.

Section	Documents
Balances	Year-end statements for every account including rarely used ones, year-end loan statements with total interest, receivable and payable agings, inventory count
Assets	Invoices for every asset bought, bill of sale for every asset sold, vehicle details, improvement invoices
People	Final payroll register and year-end slips, contractor list with totals, W-9s or Canadian details for anyone missing
Tax	Sales tax reconciliation, estimated payments made, property tax bills, every agency letter from the year
Entity	Board minutes, ownership changes, new agreements signed, insurance renewals
Questions	Business use of vehicles, home office, personal expenses paid by the business, loans to or from owners, anything unusual

Format matters as much as the document

Half of all "wrong document" problems are really format problems. Say which format you want on every item.

Document type	Ask for	Do not accept	Why
Bank, card and loan statements	PDF downloaded from the bank's website	Screenshots, CSV exports, bank feed	Only the statement has opening and closing balances and page numbers
Payout, payroll and aging reports	PDF, Excel or CSV export from the software	Screenshots, a typed summary	You need the detail rows, and the export names the report and period
Receipts and bills	Photo or PDF with date, vendor, total and items readable	Card terminal slip alone	The slip shows the amount, not what was bought
Agreements and leases	Full signed PDF, every page and schedule	First page only, unsigned draft	Terms live in the schedules; unsigned means nothing
Tax notices and filings	Every page of the letter or filed return	Photo of the envelope or the first page	The amount due and the reason are usually on page two
Lists and answers	A form answer or a spreadsheet	A sentence in an email	You can act on structured data

The IRS and CRA both accept electronic records, with conditions, and their general retention rules are 3 years (IRS, longer in several situations) and 6 years from the end of the last tax year the records relate to (CRA). The monthly bookkeeping checklist links the official pages; point clients there rather than promising that a photo always replaces the paper.

The master checklist in Tangentflow, step by step

A PDF of this list is a fine reference to attach to the engagement letter, but it is a poor collection tool, because nothing tells you or the client what has arrived. Tangentflow collects documents through one private link per request, checks every upload as it arrives and has an AI collection agent do the chasing by email. The plan: one master checklist with yes or no questions that hide what does not apply, split into onboarding, monthly and year-end checklists.

1. Start from the built-in templates

Go to "Checklists", choose "Browse templates" and look at the three templates that already carry parts of the master list:

• "Monthly bookkeeping": bank statements for the month, credit card statements, receipts and bills, sales or invoices issued, a payroll report and an "Anything unusual this month?" question.
• "Year-end documents": income documents, bank statements with every page required, expense receipts and an "Any changes this year?" question.
• "Audit / review PBC list": trial balance, general ledger detail, bank statements and reconciliations, AR and AP aging, fixed asset register, loan and lease agreements, board minutes, a lawsuits question and an "anything unusual" question, with the report items set to "PDF or spreadsheet."

For the onboarding request, start from scratch or from "Year-end documents" and build the onboarding sections from the tables above. You can also describe what you need in a sentence and let AI draft the items, then edit.

2. Give every item a format and a rule

Open each item in the checklist editor. Fill in "What should it be?" in the client's words ("the PDF statement from your bank's website for every business account"), set the count, and pick the accepted file type: "PDF only" for bank, card and loan statements, "PDF or spreadsheet" for payout, payroll and aging reports so Excel and CSV exports upload as readily as PDFs. Tick "every page" for statements and agreements, and add a date rule such as "dated in the last 45 days" for monthly statements.

Add an "Example" to anything clients get wrong: "A good upload is the 4-page PDF from your bank's Documents tab, not a screenshot of the app."

3. Trim the list per client with questions

Add "Form field" items for the questions that decide which sections apply: "Do you have any loans, lines of credit or equipment financing?", "Do you have employees on payroll?", "Do you sell through an online platform or POS?", "Does the business lease its premises?", "Did you buy or sell any equipment or vehicles this year?" Set "Only ask if" on the loan, payroll, payout, lease and asset items so they appear only when the answer is yes. One master checklist then fits a solo consultant and a twelve-employee contractor without either seeing the other's items.

Keep the legal, entity, loan and lease items in the onboarding checklist, the recurring items in the monthly checklist, and the balance and asset items in the year-end checklist. Private context goes in "Notes for the agent (private)" on each request, such as "Owner holds the loan agreements; the office manager sends statements."

4. Send the request

Go to "Requests", click "New request", choose the checklist, add a reference such as "Pinecrest Landscaping, onboarding" or "Pinecrest Landscaping, October 2026", the client's name and email, and a needed-by date. Leave "Email the link" on and the agent sends the invitation from your firm's name. For the monthly request across every client, use "Batches": paste your client list, pick the monthly checklist, give each client a needed-by date and turn on "Repeat every month" so it goes out again on the same day each month (bulk requests, part of Pro).

For checklists that carry payroll registers, tax notices or agreements, turn on "Require an email code": before the link opens, the client enters a 6-digit code emailed to them, so a forwarded link is not enough on its own. If a link goes to the wrong address, "Reset link" on the request stops the old one working. After the client sends everything, the link no longer shows the files.

5. Review what came in and download the Evidence index

Each upload is checked in seconds by document checks: the right document type, readable, every page, covering the right period, and for spreadsheets the first rows are read to confirm what the report is and whether it covers the month. If something is off, the client sees a friendly note while they still have the file open. Reminders are paced to the needed-by date and list only what is still missing, and the agent answers questions like "Is the loan statement the same as the amortization schedule?" from your item hints and private notes, or hands off to you.

The request page shows every file, its check result, the client's answers, what is outstanding and an activity timeline, with "Ask for changes" on any single file. When everything is in, download the organized ZIP, or on Pro deliver to Google Drive or a webhook. From the request's menu, download the "Evidence index (CSV)": one row per item and file with the status, check result, extracted facts such as the report name and period, and the client's answers. It is a ready-made record of which source documents you hold for the period. Mark the request complete and the files are deleted 24 hours later; your bookkeeping file, not the collection tool, is the system of record.

Setups by type of client

Start from the master list and the three templates, then adjust per group. Keep one checklist per group and send each group its own batch.

Client type	Sections to emphasize	Settings worth turning on	Learn more
Service business, no employees	Bank and cards, sales invoices, purchases, home office and mileage	Yes/no for loans and vehicles with "Only ask if"	Self-employed checklist
Retail or online store	Payout reports per platform, sales tax by jurisdiction, inventory	"PDF or spreadsheet" on payout items, higher max count	E-commerce reports
Trades and construction	Contracts and change orders, subcontractor invoices, equipment finance, W-9s or T5018 details	Per-job references, yes/no for new subs	Construction checklist
Clients with payroll	Payroll register, remittance reports, quarterly filings, new hire forms	"Require an email code" on the checklist	Payroll reports
Corporations with several owners	Minutes, shareholder loans, dividends, ownership changes	"Every page" on agreements in the onboarding checklist	Accounting and tax
Audit or review clients	Trial balance, ledger detail, agings, register, agreements, minutes	"Audit / review PBC list" template, Evidence index	PBC list template

When something goes wrong

Problem	Likely cause	Fix
Client sends a bank CSV or app screenshot instead of the statement	They do not know where the PDF lives	Set the item to "PDF only" and add an Example naming the bank's Documents or Statements tab
Loan agreement arrives as the first page only	Client photographed the summary	Tick "every page"; the check flags the missing schedules
A loan, lease or account appears months later	The onboarding questions missed it, or it is new	Add "Any new accounts, loans or leases this month?" to the monthly request
Payroll register is for the wrong period	Provider defaults to the current pay date	Add a date rule and an Example naming the report and date range to pick
Client says a document "doesn't exist"	Different situation than you assumed	Put the item behind a yes/no with "Only ask if"; call if the answer surprises you
Client is overwhelmed by the onboarding list	Too many items at once	Split onboarding into two requests a week apart: accounts and history first, agreements and entity second
Client is frustrated by reminders	Busy month, too many emails	The agent stops and hands off to you; reply personally and move the date

Check "Alerts" daily during onboarding and close week. That is where handoffs and missed dates show up. If a client is late every month, the late document policy guide covers what to put in writing.

Free and Pro, honestly

You can run a real request without paying anything.

	Free	Pro ($29/month)
Open requests	1 at a time	Unlimited
AI check on each file	Yes	Yes
AI autopilot (answers, reminders, follow-ups)	Your first request	Every request
Send to many clients at once (Batches)	No	Yes
Clients reply by email with attachments	No	Yes
Branding	Tangentflow badge	Your logo
Delivery to Google Drive or a webhook	No	Yes
Works with AI assistants (MCP)	No	Yes
File retention	7 days	60 days

Both plans include unlimited checklists, QR codes and posters, ZIP export, AI summaries, the Evidence index and email delivery. Pro is billed monthly with no contract, and you can cancel any time. Full details on the pricing page, and more on how files are protected on the security page.

What Tangentflow does not do: SMS or text messages, a native mobile app, full legal e-signature certificates, identity verification, collecting payments, or permanent storage. If you need any of those, pair it with a tool that does. It also does not connect to bank feeds, categorize transactions or replace your bookkeeping software.

The master document checklist as a checklist

1. Keep one master list of source documents in eight groups: bank and cards, sales, purchases, payroll and contractors, loans and leases, assets, tax, legal and entity.
2. For each document, know why you need it and how often: onboarding, monthly, quarterly, year-end or as it happens.
3. Add the industry add-ons for restaurants, construction, nonprofits, self-employed, online sellers and rental properties from their own checklists.
4. Split the master list into three standing requests: onboarding, monthly and year-end. Never send it as one email.
5. Trim per client with four or five yes or no questions rather than editing the list by hand.
6. Name the format on every item: PDF only for statements, PDF or spreadsheet for reports, readable photos for receipts, every page for agreements.
7. Treat tax agency letters and new accounts, loans or leases as same-day items, not monthly ones.
8. Check every file on arrival, keep an index of which source documents you hold for each period, and move the files into your system of record.

Sources

Official pages for the forms and rules named in this guide. Links checked on October 24, 2026; rules and rates change, so confirm on the official page before relying on them.

• CRA, GST/HST for businesses: registering, charging, filing and input tax credits
• IRS Form 941: employer's quarterly federal tax return
• CRA Form T5018: statement of contract payments
• IRS Form 1040-ES: estimated tax for individuals
• IRS Form 8821: tax information authorization
• IRS Form 990: return of organization exempt from income tax
• CRA Form T3010: registered charity information return
• IRS Form 1098: mortgage interest statement

Frequently asked questions

What documents are needed for bookkeeping?

Bank and credit card statements for every business account, sales records such as invoices and platform payout reports, supplier bills and receipts, payroll reports and contractor details, loan and lease agreements with their statements, invoices for assets bought and sold, tax filings and any letters from a tax agency, and the entity documents that describe the business. Most clients send the first four groups monthly and the rest at onboarding and year-end.

What is a source document in bookkeeping?

A source document is the original evidence that a transaction happened and what it was for: an invoice, a receipt, a bank statement, a signed agreement or a payroll register. Your bookkeeping software holds the entries; source documents prove the entries are right when a lender, an auditor, the IRS or the CRA asks.

Is a bank feed enough, or do I still need statements?

You still need statements. A bank feed can drop or duplicate transactions and has no opening or closing balance, so there is nothing to reconcile to. Ask for the PDF statement from the bank's website every month, or get read-only accountant access and download it yourself.

What should a new bookkeeping client send first?

The entity documents, a list of every account with a statement for the month before your start date, the prior-year return, every loan agreement with its amortization schedule, the premises lease, insurance policies, the employee and contractor lists, and access to the payroll and sales platforms. Our onboarding checklist for accounting firms puts these in order with a 30-day plan.

How often should clients send bookkeeping documents?

Statements, sales reports, bills, receipts and payroll registers monthly. Sales and payroll tax filings each filing period. Loan statements monthly for lines of credit and at least yearly for term loans. Agreements, entity documents and asset invoices when they are signed or bought, with a year-end review to catch anything missed.

How long do clients need to keep bookkeeping source documents?

The IRS general rule is 3 years, with longer periods in several situations such as employment tax records and unreported income. The CRA general rule is 6 years from the end of the last tax year the records relate to. Both accept electronic records with conditions. Check the official IRS and CRA pages and the client's advisor for their situation.

Can I collect all of these documents through one link?

Yes. In Tangentflow, one master checklist with yes or no questions and "Only ask if" shows each client only the sections that apply, split into onboarding, monthly and year-end checklists sent through one private link per request. Each file is checked on arrival, the agent chases what is missing by email, and the Evidence index gives you a CSV record of every source document received. Read how bookkeepers use Tangentflow, or try it free with one client.