Sometimes when we open a signed PDF, Adobe Acrobat Reader tells us “The validity of the document’s certification is unknown. The author cannot be verified“, visible in the Signature Panel and in the signature seals (if any), because Adobe does not trust the Certification Service Provider that issued the certificate (for example FNMT, Camerfirma, Firmaprofesional, Avansi…) To solve it, we only have to configure it to trust the issuer of the certificate. In this link we explain the steps to follow.
