I had problems with digitally signing documents in Acrobat Reader 2023.003 via a certificate on a smart card. Whereas in Acrobat Standard 2017 the digital signature worked correctly, in Acrobat Reader DC an error message popped up: Error in BER decoding, and the signature, which was visible in the document was not valid. The Adobe support recommended using a solution by re-creating the digital ID and/or Crypto folder (see https://helpx.adobe.com/acrobat/kb/error-creation-signature-could-completed.html). But this did not solve the problem. By further internet search I found a discussion in the Adobe Community which recommended:
Go to Preferences of Adobe: Edit/Preferences/Security (Enhanced):
Enable Protected Mode at Startup: deactivate checkbox;
Protected View: Off;
Enable Enhanced Security: activate checkbox;
Automatically trust documents with valid certificate: activate checkbox;
Automatically trust sites… : activate checkbox;

In the default settings in my company the checkbox “Enable Protected Mode at Startup” was activated. The other settings were as recommended. After deactivating the checkbox and closing and reopening Acrobat Reader I could add a valid digital signature with my smart card certificate.