Open the PDF in a PDF reader that supports digital signatures
Locate the signature field or signature panel
Check whether the signature status shows valid, invalid, or unknown
Verify that the certificate chain is trusted
Confirm that the certificate was issued by a trusted certificate authority
Check that the certificate is not expired
Check that the certificate was not revoked
Verify the document has not been modified after signing
Confirm the signing time is within the certificate validity period
Validate the document integrity hash
Check the signature algorithm is supported and secure
Verify any timestamp token if present
Confirm the signer identity matches the expected signer
Use a trusted validation tool or library for programmatic verification
Review any warning messages from the PDF viewer or validator