When opening a signed PDF file, Adobe Acrobat Reader may display the following error message when checking the electronic signature: “There is at least one signature with problems”. In newer versions of Adobe Reader, this message will be displayed as:“The validity of the document certification is UNKNOWN. The author cannot be verified.” This message appears in the Signature Panel and in the signature stamps (if any).This is because Adobe Reader does not have the Certificate Authority that issued the certificate to sign the pdf (for example FNMT, Camerfirma, Firmaprofesional, Avansi…) identified as a trusted issuer.To solve the error “There is at least one signature with problems”, we will configure Adobe Reader to trust the issuer of the certificate to validate the digital signature.In the following link you have a guide with the steps to follow: Managing trusted certificates in Adobe Reader.
