PDF files is opened by Excel

My customer running W98 said he downloaded some Windows updates a week ago. I asked him if it was from the Microsoft site and he said it was. He does not know if he has auto update enabled but a window popped up and asked to update. He described the update site to a T without me coaching. He was able to download Adobe PDF files in the past and they would open now when he downloads they open in Excel and are not legible. I tried to use open with but it does not appear on his R click menu. I tried folder options but this is going to associate all files of Excel type to open with Adobe.
I dont know if there is a known hijack program that these updates installed.
Any help.