As per the description above, the users with Adobe Reader DC are not able to sign a PDF with certificates, Is that correct? To sign a document with a certificate-based signature, you must obtain a digital ID or create a self-signed digital ID in Acrobat or Adobe Reader. Ask t...
So if using a self-sign certificate works, and everything is up to date, then you can assume that the smart card reader could be bad. Try connecting a new or just another smartcard reader and see if that happens again. Worst case scenario would be, that the ...