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Building an Audit Trail: A Practical Example

This example follows a small business building a defensible audit trail for 200 supplier invoices across a quarter. Manually, the audit trail is a shoebox of PDFs in a shared drive with no link between the source document and the accounting entry — reconstructing it for an audit takes days. With Nika each invoice is archived with its source email, extraction data, and coded entry linked in a single chain at {price} per processed invoice — the audit trail is built continuously, not reconstructed under pressure.

Before: manual process

A 15-person marketing agency needs to produce an audit trail for its Q1 supplier invoices — roughly 200 invoices totaling €85,000. The tax authority has requested documentation for a sample of 30 invoices as part of a routine review. The bookkeeper enters invoices into the accounting system, but the source PDFs are stored inconsistently: some in a shared Google Drive folder organised by month, some still in the original email threads, some on the bookkeeper's personal laptop. There is no link between the PDF and the accounting entry — finding a specific invoice means searching the drive, the inbox, and the laptop, then matching the amount to the ledger. For 30 invoices, the bookkeeper estimates two full days of searching, matching, and assembling a documentation pack. Three invoices cannot be found at all.

After: with Nika

The same agency uses Nika. When each of the 200 invoices arrived during Q1, Nika read it, entered the fields, coded the category, and filed the source PDF — all in one action. The audit trail is built continuously: each accounting entry is linked to its source email, the extracted data (vendor, date, amount, VAT), the original PDF, and a timestamp of when it was processed. When the tax authority requests documentation for 30 invoices, the bookkeeper runs a query and exports the 30 entries with their linked source documents in 15 minutes. Every invoice is accounted for, every entry is traceable to its source, and the documentation pack is complete. Cost: {price} per processed invoice — the audit trail is a byproduct of normal processing, not a separate project.

Workflow

  1. 1

    Source capture

    In: Supplier invoice email — subject, sender, timestamp, PDF attachment
    Out: Email metadata + PDF archived together as the source record
    Saved: Eliminates manual filing — source captured at receipt, not reconstructed later
  2. 2

    Extraction record

    In: PDF invoice — vendor, date, number, net, VAT, total
    Out: Extracted fields stored alongside the source PDF as a verifiable extraction record
    Saved: Eliminates manual data matching between PDF and ledger entry
  3. 3

    Entry linkage

    In: Coded accounting record + source email + extraction data
    Out: Single linked chain: email → PDF → extracted fields → coded entry → filed record
    Saved: Audit retrieval becomes a query (15 min) instead of a search project (2 days)
  4. 4

    Export on demand

    In: Tax authority request for 30 sample invoices
    Out: 30 entries exported with linked source documents in a single pack
    Saved: Documentation pack assembled in minutes, not days

Cost comparison

MethodCostTime
Manual — bookkeeper reconstructs trail (€18/hr)~€600 / audit request (2 days × €300/day equivalent)2 full days per audit sample
Outsourced accountant (documentation pack)Typically €400–800 per audit response1–3 days turnaround
Nika (per processed invoice — trail built continuously){price} / invoice × 200Audit export: 15 minutes

Key takeaways

  • The audit trail is built as a byproduct of normal invoice processing — not as a separate project triggered by an audit request.
  • Every accounting entry is linked to its source email, original PDF, and extracted data in a single verifiable chain.
  • Audit response time drops from days of searching to a 15-minute export query.
  • No invoice goes missing — the source document is captured at receipt, not chased down months later.

Questions

What exactly is in the audit trail for each invoice?

For each invoice, the trail contains: the original source email (sender, date, subject), the PDF attachment, the extracted data fields (vendor, invoice date, invoice number, net amount, VAT, total), the coded expense category, and a timestamp of when the entry was created. This chain lets an auditor verify that each accounting entry corresponds to a real source document, entered accurately, on a specific date.

How long are the source documents retained?

Source documents (emails, PDFs, extraction records) are retained for as long as your accounting system retains the entries — typically matching the statutory retention period in your jurisdiction (6 years in the EU and UK, 3–7 years elsewhere). Nika does not set the retention policy — your accounting system and data retention configuration do. She ensures the documents are captured and linked so they are available for the full retention period.

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