Signature issues

I have a staff member trying to do a certificate-based signature to a PDF in Acrobat Pro. She signs the same file every two weeks and now she is unable to sign the same file like normal. When she goes to sign, she walks through all the steps and then the wait clock stays on her screen for hours and does not actually add the signature. She is able to sign one page files with no problems but once she tries to sign one page on a multiple page file, this is when it freezes. I am not sure why out of the blue it is not liking this file as it is the same size as it was before.