When you open a document that is digitally signed checks the document, then the certificates and lastly the revocation list online before stating if it's valid or invalid. I would suggest not to check every time since one may open and normally open the same doc many times in the same day, sometimes the same hour, forcing the process once and again for each file. As we do with the passwords for buying once every 15 min, 30 min, a day is sufficient if not on request to do all that process, nothing really changes in that hour.
To keep in consideration.
Security digital signatures and esignatures