Hi, It's much the same way as in my previous post.
Find any file ( on your PC) that you know to be a .pdf, right-click on it, and the last choice in the list is 'Properties', click on that one.
In the next box, look at the second section down, "Type of file: Opens with;" and then click on the box "Change".
Another box will open with all of the programs on your PC that will open a .pdf file, so then you just choose the one you prefer.
( I have found pdf x-change viewer to be very good.)