PDF signature checker

A digitally signed PDF contains a cryptographic signature that binds the document's content to the signer's certificate. If anyone changes the signed content afterwards, verification fails. This checker reads the signatures embedded in a PDF and shows who signed it, when, and whether the signed content is still intact.

How to use it

1. Select a signed PDF file.
2. Review each signature found: signer name, certificate issuer, signing time and integrity status.

How PDF signatures work

The signature covers specific byte ranges of the file, everything except the signature value itself. A hash of those bytes is signed with the signer's private key and stored together with their certificate, usually in a PKCS#7 or CMS container. Verification recomputes the hash and checks it against the signature using the certificate's public key.

Understanding the results

• Integrity valid: the signed bytes have not changed since signing.
• Certificate chain: whether the certificate was issued by a trusted certificate authority. A self-signed certificate proves integrity but not identity.
• Signing time: taken from the signature; a trusted timestamp (TSA) is stronger proof than the signer's own clock.
• Incremental updates: PDFs can legitimately be modified after signing, for example by adding another signature or filling a form field. Check whether later changes are allowed.

Digital vs. electronic signatures

A drawn or typed signature image is an electronic signature but offers no cryptographic protection. Only certificate-based digital signatures, such as those from Adobe Acrobat, DocuSign or government e-signing services, can be verified this way.