Windows 7 allows users to change and set default program association for most kind of file extension under Control Panel –> Default Programs –> Set Associations. There are is no option or a way to reset fact to when the Windows installed but we have some workarounds.
Unless user remembers and knows the original file association and change the default program for the kind of file type accordingly using the graphical user interface (GUI) in Control Panel. Here is another workaround to restore or reset the file association to the defaults in Windows 7.
1. Press the Windows key + r (or Click Start Menu, and then type regedit)
2. Navigate to the following registry branch in registry:
Here you will find all the extensions for that version of Windows and you can replace with the program of your choice, assuming that exist in your computer.
3. Delete the sub-key named UserChoice.
4. Exit from Registry Editor.
5. You are done!