How was the PDF signed (manually with Acrobat, or using a LiveCycle process)?
Assuming you are using the "Verify PDF Signature" operation, what is the "Revocation Check Style" set to?
NoCheck:
Does not check for revocation.
BestEffort:
Checks for revocation of all certificates when possible.
CheckIfAvailable:
(Default) Checks for revocation of all certificates only when revocation information is available.
AlwaysCheck:
Checks for revocation of all certificates.
Thanks
Steve