When we open a signed PDF, Adobe displays an error message:
”At least one signature has problems”
In the new Adobe Reader version, this message will be prompt as follows:
”The validity of the document certification is UNKNOWN. The author could not be verified”
This message is shown in the signature panel and in signature stamps ( if any)
This is because the trusted service that issued the certificate isn’t in the Adobe Authorized Trust List (AAT) (for example FNMT, Camerfirma, Firmaprofesional, Avansi…)
To fix this, configure Adobe Reader to trust the Certificate issuer. You can check our guide where we explain the steps to follow in Trusted Certificates Management in Adobe Reader