When validating a digital signature or timestamp, the status may show as “unknown” or “could not be verified.” To resolve this, add the issuing certificate and the timestamp server to your Trusted Certificates list.

A trusted time stamp proves that the contents of your PDFs existed at a specific point in time and have not changed since then. Foxit PDF Editor allows you to add a trusted time stamp to digital signatures or documents.

The document author can certify their own PDF documents. The author can specify what changes can be made to the file after certifying.

For a digitally signed document (which might have been signed several times), you can view the differences (if any) between a signed version and the current version you have.

A signed version will be automatically saved each time you sign a PDF with a digital signature. If a digitally signed document was modified, you can still view the signed version without the modification.

Many business or other practical applications need digitally-signed documents to be verifiable for months or years after signing. To reduce chances for error or fraud, Long Term Validation (LTV) is introduced for digital signatures in PDFs.

Validate a signature by selecting it through any available method (Protect > Validate, right‑clicking, or using the Digital Signatures panel). A Signature Validation Status message box then appears, showing the result.

By default, Foxit PDF Editor will check the certificate revocation status while validating a signature if the certificate used to sign a PDF file chains up to a certificate designated as a trusted anchor.

By default, Foxit PDF Editor verifies signatures when the document is opened. The signature state appears in the Signature Panel.

The signature of a certified or signed document is valid if you and the signer have a trust relationship. The trust level of the certificate indicates the actions for which you trust the signer.