Internal Document Systems and Preparing for Your Accounting Firm: The Heart of Managing a Legal Entity

Starting accurate bookkeeping is not only a legal duty that begins immediately after a legal entity is registered; it is also an important tool for understanding the business’s true financial position.

An orderly internal document system helps the accounting firm record transactions accurately and allows the financial statements to be audited smoothly by a CPA or TA.

1. Key Types of Internal Accounting Documents

Internal documents provide evidence of money moving through the organization. The main types are:

• Receipt Voucher: records payments received from customers and confirms cash or bank transfers together with the receipt issued, allowing the accounting firm to verify complete income records.
• Payment Voucher: records every payment made as an operating expense. Attach evidence such as a purchase tax invoice, supplier receipt, or substitute receipt certificate to prove the transaction relates to the business.

Voucher type	Used when	Evidence to attach
Receipt Voucher	Company receives money from a customer	Receipt / transfer evidence
Payment Voucher	Company pays an operating expense	Purchase tax invoice / supplier receipt / substitute receipt certificate

2. Preparing Supporting Documents for Bookkeeping

In addition to internal vouchers, business owners should collect the following external evidence for the accounting firm:

• Tax documents: full tax invoices for purchases and sales to support monthly ภ.พ.30 filings, plus all types of withholding tax certificates such as ภ.ง.ด. 1, 3, and 53
• Bank documents: bank statements for every account in the company’s name. Keeping a separate company bank account reduces confusion and supports accurate cash reconciliation.
• Employee and benefits documents: payroll and monthly evidence of social-security contribution remittance

3. Statutory Duties and Retention

The Accounting Act B.E. 2543 imposes strict duties on legal entities for managing these documents:

• Recording period: the business must record accounting entries within 3 days of the transaction date
• Document retention: accounting-supporting documents and original tax invoices must be stored securely at the head office for at least 5 years, and in some cases up to 7 years

4. Efficient Handover to Your Accounting Firm

To close the financial statements quickly, business owners should deliver the document set to the accounting firm every month according to the agreed schedule.

Using an online accounting program connected to the accounting firm reduces paper handover and lets the auditor review information immediately through the cloud, reducing the risk of missing documents and late-filing penalties.

In summary, directors are directly responsible for establishing a transparent document system that builds credibility and reduces long-term tax risk.

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