Error when signing a PDF with a certificate

[ingoprz]

I am using a personal certificate, issuded from the DFN to sign my mails and documents.

On a freshly installed Mac,  using this certicate results in the following error messsage (sorry, sionce I use the German version, I can only provide the german error) : "Beim Unterschreiben ist ein Fehler aufgetreten: Die für das Unterschreiben ausgefüllte Referenz ist ungültig"  Freely translated this means sometihng like "An error has occurred while signing: The reference filled in for the signature is invalid" 

I use the same certificate on other Macs with Arcrobat Reader to sign documents and on the affected computer I use this certificate to sign Emails. Anything works with this exception (signing pdf doctuments on this mac with Adobe Reader DC)

Any help would be very appreciated