For XP, I would assume other OS's are similar.
Go to the file in Windows Explorer.
Right click, select properties
On the General tab, select Change for Opens with.
That changes the association.

>Hi all.
>
>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).
>
>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.