---
id: KB-GL-006
url: https://app.codecontract.io/help/glossary/what-is-a-document-hash
idioma: en
categoria: glosario
subcategoria: firma
audiencia: usuario
nivel: intermedio
actualizado: 2026-08-13
tambienEn: [es]
relacionados: [KB-GL-005, KB-TZ-002]
citadoPor: [KB-GL-005]
---

# What is a document fingerprint

_A short number that changes if a single comma in the document changes._

**Responde a:** what is a file hash · document digital fingerprint · how to tell if a pdf was modified · sha256 document

**Hash (fingerprint)** — A short value calculated from a file's entire content, such that any change to the file — however small — produces a completely different value.

It is what lets you check a document has not changed without keeping a copy to compare against. Storing the fingerprint, a few dozen characters, is enough.

## The three properties that make it useful

**En corto**

- The same file always yields the same fingerprint.
- Changing one comma yields a completely different fingerprint, not a similar one.
- The document cannot be reconstructed from the fingerprint.

The third matters more than it seems: you can publish the fingerprint of a confidential contract without revealing anything about its content, and still prove later that it is the same contract.

> [!NOTE]
> When verification says "does not match", it is almost never fraud: reprinting a PDF, re-saving it from another program or converting it changes the file. Change the file, change the fingerprint.

**Can two different documents share a fingerprint?**

With the algorithms in use, not in practice.

**Does the fingerprint say what changed?**

No, only that something changed. To know what, compare the two versions.

**Do I need to understand this to use it?**

No. Verification tells you "matches" or "does not match".

## Ejemplos

**Two parties want a record of a confidential agreement without showing it to anyone.**

- Seal the document
- Share only the fingerprint with a third party

→ They can later prove the agreement is exactly that one, without having revealed its content.

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

- Compares the received fingerprint with the registered one

→ The check does not require reading it through.

**A comma is changed in an already sealed contract.**

- Checks that the fingerprint no longer matches

→ Any change is detected, however small.

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

- Computes the fingerprint of both

→ The original is identified without opening a dispute.

**A document's existence must be proved without disclosing it.**

- Shares only its fingerprint

→ The proof travels without the content.

**A third party wants to verify a document that reached them another way.**

- Tells them how to check the fingerprint themselves

→ Verification does not require trusting whoever sent it.