Many business or other practical applications need digitally-signed documents to be verifiable for months or years after signing. However, the signed document can be no longer verifiable if the signer’s certificate has expired or been revoked, or with some other reasons. To reduce chances for error or fraud, Long Term Validation (LTV) is introduced for digital signatures in PDF, which is in compliance with Part 4 of the ETSI TS 102778-4 PDF Advanced Electronic Signatures (PAdES) standard.
When LTV is enabled, the document can be validated at any time in the future. To achieve long-term validation, the following are required:
- The signature is verified using the secure time provided by a timestamp or at which the signature was applied.
- The signed PDF has not been altered and the certificate has not been revoked or expired.
- The certificate revocation status is embedded in the signed PDF. Embedding certificate revocation information can occur when the document is signed and saved.
From the Signature panel, you can check whether the signature is LTV enabled or not after validation. In some cases, the certificate revocation information may not be embedded successfully in the document when you sign the document (especially when you are offline) and you will be informed the signature is not LTV enabled. You can right-click the signature and choose Add verification information to add the information to the signature.
Note: To use secure time for verification, after clicking Change Settings for Singing & Verifications in File > Preferences > Signature, select the Time at which the signature was created, or Secure time (timestamp) embedded in the signature if a trusted timestamp is embedded.