All PDF's on computer getting "Acrobat could not open" errors after update

Hi, I have a computer that after a worker did some "update", all PDF files get an error message, "acrobat could not open "file name" because it is either not a supported file type or because the file has been damaged.

I had a backup of one file and opened it and the damaged file in note pad.  The original had a header and footer in plain English, with a body of coding stuff.  The damaged one (in note pad) had no such understandable verbiage.

PDF files created after this update, or what ever open fine, just the old ones are toast.

Thanks in advance for the responses.