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PDF Signing Guide
Whenever you open a digitally signed PDF, you can check whether the signature is genuinely valid, who signed it, when, and whether the document has been changed since.
Adobe automatically validates signatures when you open a signed PDF, but here's how to check the details yourself.
When you open a digitally signed PDF, Adobe Acrobat Reader shows a signature panel or a blue bar at the top indicating signature status.
Click directly on the visible signature on the page, or open the Signature Panel from the left sidebar.
A blue ribbon icon means the signature is valid and the document hasn't been modified since signing. A red/warning icon means there's a problem, either the certificate isn't trusted, or the document was changed after signing.
Click 'Signature Properties' for full details, the signer's name, the Certifying Authority that issued the certificate, the exact time of signing, and the certificate's validity period.
If Adobe shows the signer's identity as unverified, it may mean the issuing CA's root certificate isn't yet trusted on your system, Adobe usually resolves this automatically for licensed Indian CAs, but you can manually add trust if needed.
A valid digital signature on a PDF confirms three things: the identity of the signer (verified by the Certifying Authority at the time of issuance), that the document has not been altered since it was signed, and the exact time of signing (especially important when a timestamp server was used).
This is fundamentally different from a scanned signature image, which proves none of these things and can be copy-pasted onto any document.
If you're checking signature validity because you're about to start signing documents yourself, here's where to start.
This usually means the document was edited after signing, or the signer's certificate has since expired or been revoked. A genuinely unaltered, validly signed PDF will show a blue valid-signature icon.
Most modern PDF readers with certificate support (not just Adobe) can validate digital signatures, though the exact interface differs.
Not necessarily, if the PDF was signed with a timestamp while the certificate was still valid, the signature typically remains valid even after the certificate later expires.