Digital Signature and Digital Certificate Signing are not working

@hani_HFK The error message about the credential being invalid can sometimes point to a mismatch between the certificate and Acrobat’s security settings, or even a permissions issue on your Mac. Unfortunately, I can't duplicate this error message on my end as it works perfectly fine for me... which of course doesn't help you. 

You can try the following then:

• Even though your certificate looks valid (not expired and properly issued), Acrobat might not be using the correct one for signing. Try manually selecting the certificate again when signing, and make sure it’s the one listed under “Digital Signature” and “Non-Repudiation” usage.
  
  
• Since your certificate is stored in the Mac Keychain, Acrobat needs permission to access it. Sometimes, macOS security settings block this. You can check this by opening the Keychain Access. Look for your certificate. Right-clicking it → Get Info → Access Control tab. Make sure Acrobat is listed as an allowed app, or set it to “Allow all applications to access this item” temporarily for testing.