Vermutung, kann es daran liegen, dass beim Signatur-Algorithmus SSA-PSS Padding genutzt wird?
Do you use a smart card that has your signing credential and you use Windows CNG? I've seen examples when the smart card driver did not properly process correctly and did not return all required info and that made Acrobat to not be able to sign. I used Google to translate your text so I may not understand your problem correctly.
thanks so much for your answer.
Actually we are using our own software which is not restricted to windows or its crypto api. And there is no difference between signing with a smartcard or using a software certificate.
The difference is when using pss padding as signature scheme. When pss padding is not used for signature creation Adobe Reader has no problem with the signature and the error doesnt occur.
Unfortunately RSAPSS padding was introduces and recommended years ago and it seems that this is one of the reasons for the error.
Error signature verifcation
An error occured during validation:
Internal cryptography error in the library.
Error Code: 0x20C
The error text makes me to think that it is Windows Cryptography Services that cannot process the request. It is also possible that Acrobat does not support RSAPSS padding. In this case you can submit a feature request to Adobe to fix it.
But the error code as well as the error text is the same in Adobe Reader DC or Adobe Acrobat on Mac OSX.
And yes we will submit a feature request to Adobe.