Tamper seal

When a document is finalized, QSign applies a tamper seal — a cryptographic (CMS) signature over the finished PDF. If even a single byte changes afterward, signature verification fails, so any later modification is detectable.

• The seal is computed over the finalized bytes and recorded alongside the document hash, the seal timestamp, and the signature method — the basis of the evidence trail.
• For maximum third-party trust (a green “valid” in Adobe Reader without manual trust), an organization can configure a signing certificate from a recognized CA.
• A self-signed seal still provides full tamper-evidence, but some readers show a yellow “not trusted” banner until the signer’s CA chain is trusted — this does not affect the legal validity of the signature.

See also Audit trail.