---
id: KB-TZ-002
url: https://app.codecontract.io/help/traceability-and-compliance/proving-a-document-has-not-changed
idioma: en
categoria: trazabilidad
audiencia: usuario
nivel: intermedio
actualizado: 2026-08-13
tambienEn: [es]
relacionados: [KB-TZ-001, KB-SC-001]
citadoPor: [KB-DI-006, KB-SC-004, KB-SC-005, KB-SC-008, KB-TZ-008, KB-NO-001, KB-TZ-009, KB-TZ-010, KB-SC-010, KB-LE-007, KB-TZ-004, KB-TZ-005, KB-GL-005, KB-GL-006, KB-CF-003, KB-CF-008]
---

# Proving a document has not changed

_How to check it, who can, and why it works without trusting us._

**Responde a:** verify a document is authentic · check whether a pdf was modified · what is a timestamp · verify a document without an account

A sealed document can be checked without entering the platform, without an account and without asking our permission. That is the important part: if you had to trust us, it would not prove much.

**En corto**

- Every document has a fingerprint that changes if a single character changes.
- The time is certified by an independent third party, not by our server.
- Anyone holding the document can check it.

## How to check

1. **Go to the public verification page.**
2. **Upload the document, or scan its code if it carries one.**
3. **Read the result: it matches or it does not.**

## What each result means

| Result | What it means |
| --- | --- |
| Matches | It is exactly the document that was sealed, on the date stated |
| Does not match | The file has changed since then, even by a comma |
| Not found | That document was never sealed here |

> [!IMPORTANT]
> "Does not match" does not necessarily mean fraud. Reprinting a PDF or re-saving it from another program changes the file. What it does mean is that this particular file is not the one that was sealed.

## Why someone else sets the time

If we set the date, you would have to trust our clock. It is set by an independent timestamping authority, and its signature can be checked separately. That is the difference between saying "it happened on Tuesday" and being able to prove it.

**Do I need an account to verify?**

No, and that is deliberate: whoever verifies is usually an outsider.

**Will it still work in ten years?**

Yes, as long as you keep the document. Verification does not depend on you having an account.

**What if I lost the file?**

If you are in the organisation, it is stored. If you are a third party, ask whoever sent it.

## Ejemplos

**A client suspects the amendment they received is not the one agreed.**

- Uploads their copy to the verification page

→ It matches what was sealed on the signing day, and the suspicion is closed in thirty seconds without argument.

**Somebody forwards a document and it must be established it is the same.**

- Compares the fingerprint with the registered one

→ The check does not require reading it through.

**Two copies look identical and one has been altered.**

- Computes both fingerprints

→ The original is identified.

**A third party wants to verify it themselves.**

- Points them to the verification page

→ They verify without depending on you.

**The file was opened and re-saved.**

- Checks against the untouched original copy

→ Verification comes out correct.

**You want to prove it without revealing the content.**

- Shares only the fingerprint

→ The proof travels without the document.