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Adobe Reader says “Signature validity is unknown”

Why Adobe shows a warning on SignSpry-sealed PDFs, why it does not mean the document was changed, and how to check it.

Open a document sealed by SignSpry in Adobe Acrobat or Adobe Reader and you may see a yellow bar or a question mark next to the signature. It does not mean the document was changed.

What you see

  • A bar at the top: At least one signature has problems.
  • In the signature panel: Signature validity is UNKNOWN.
  • In the same panel: Document has not been modified since this signature was applied.

Why

Adobe shows a green tick only for certificates issued by a company on its own trusted list (AATL). SignSpry seals documents with its own certificate, so Adobe cannot confirm who the signer is. It still checks the seal itself, and that is the line that matters: if anything in the file had changed, Adobe would say the document was altered or corrupted.

How to check a document

  1. Go to the Verify page and upload the PDF. It checks the seal, shows the fingerprint of the certificate inside the file and confirms when it is SignSpry's seal.
  2. Compare that fingerprint with the one on the Trust & security page.
  3. Read the certificate of completion at the end of the PDF: it lists who signed, when and how.

The seal also carries an independent RFC 3161 timestamp. See Trusted timestamps.

Trusting the certificate in Adobe (optional)

If your organisation receives many SignSpry documents, you can add SignSpry's certificate to Adobe once:

  1. Download the certificate (.pem) from the Trust & security page and check its fingerprint.
  2. In Adobe, open Preferences → Signatures → Identities & Trusted Certificates, choose Trusted Certificates, then Import, and select the file.
  3. Allow it to be trusted for signed documents.

Menu names differ a little between Adobe versions. Do this only with a certificate whose fingerprint matches the one on our Trust page.

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