Document Integrity: Signed Files and Tamper Evidence

Preserving and checking signed content against unauthorized alteration, distinct from whether its statements are true.

Published on

2026-11-06

Last updated on

Integrity concerns unauthorized alteration, not the truth of the original content.
Tamper evidence supports detection; it does not make modification impossible.
Preserve the signed original before producing flattened or redacted derivatives.

What is document integrity?

For a signed file, document integrity concerns whether its content has been altered in an unauthorized way. NIST’s data-integrity definition addresses changes during creation, transmission and storage. It is distinct from the accuracy or completeness of the original statements: an unchanged document can still contain an error.

Tamper evidence versus tamper prevention

Tamper-evident means alterations can be detected using the relevant mechanism. It does not mean no one can modify, replace or copy the file. “Tamper seal” is sometimes used for an integrity mechanism; check what it covers rather than assuming an absolute guarantee.

A cryptographic hash can support comparison with a trusted reference value. If someone simply changes a file and supplies a new hash alongside it, the hash alone does not establish which version is authentic. A digital signature can bind signed data to a signing key and support checks on the covered content.

What about changes after signing?

PDF signature checks depend on the signed version and permitted later actions. PDF Association’s technical note on digital signatures explains incremental updates, including additional signatures that can preserve the data covered by an earlier signature. A changed file is therefore not automatically the same as an unauthorized rewrite.

Conversely, flattening or redacting signed content can remove or invalidate signature evidence. Keep the original signed file and review any derivative separately.

Integrity is one part of the evidence

Integrity checks do not by themselves prove who intended to sign or whether that person had authority. Preserve the related signing evidence; the electronic-signature verification guide covers the practical review.

A Common Case: Reviewing a revised signed agreement

For a California legal-services practice, a received agreement might look unchanged even after file processing. Staff could preserve the original and review its signature information before accepting a rewritten copy as the signed record, keeping the visual appearance separate from integrity checks.