Try right clicking on the file you'd like to edit with EditPad pro while holding down the shift key. The menu will now include an option called 'Open with', choose browse and navigate to and choose EditPad Pro.
This may not make edit pad the default application to edit that type of file with, but it will add it as one option when right clicking.
I believe there's another way to set this, but can't recall it right now. Aside from that, there may be options you can set for this within EditPad Pro?
"How did a fool and his money get together in the first place?"