I would try to uninstall and reinstall Acrobat Reader.

>Everytime i want to open a .PDF document i must specify which type of file is it and which program i should use to open it, how do i enable the "Use this program as default to open this type of file" (that's what i think it says).
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>Everytime i have to right-click and select "Open With" option and look for the proper application to open .PDF files, is there a way to enable this option so i can check it?? it always appear disabled. I'm using Windows XP Profesional edition.