I have been using digital signatures on PDF documents for about 10 or 15 years no problem. I sign batches of documents, and the most efficient way is to load an existing (signed) document that is close to what I want, then clear the signature, amend the document and then resign the document. for the next document, rinse and repeat.
About two months ago, Acrobat did not offer me the option of clearing the signature. After some frustration, I created a new document from scratch and attempted to sign it. It then asked me for my Id File. AHA! I thought. It has lost my Id File. So I pointed it at my Id File, and signed the document, and after that everything was fine. However, the next day, same thing again. It is as though it forgets all about my Id file the moment I shut it down.
No, nothing changed during the period. Same version of Windows (10), same version of Acrobat (XI) same computer, and same me.
Greatly appreciate any advice. It is driving me nuts, especially when I am in a hurry and the client is breathing down my virtual neck.
Sorry for the inconvenience caused and sorry for the delay in response.
Launch Acrobat>help>Check for updates and try installing pending updates Adobe - Acrobat : For Windows
A couple of users reported this issue and couldn't reproduce this in-house. However, one of the users got this fixed after launching Reader/Acrobat with admin rights and browsing for the license file again. After then it worked fine.
I would suggest installing any pending updates restart your machine and try again. Let us know if that helps.