Each file extension in Windows is associated to a program and when you open the file, its set to open with the default program for that particular extension. You can set/change the association of each extension with any program manually. To do this Open Control Panel and select “Make a file type always open in a specific program” option under Default Programs.

default programs

Here you can see the list of all extensions and the associated programs on the right.

change file associations

If you need to change or set the default program, select the extension and click Change Program button located on the top right corner.

file associations

Here the recommended programs and also the other programs are displayed. Once you select a program, the file will be associated with that program. Alternatively if you need to change only for a particular file, right click on the file and select Properties-> General Tab and select the Change button.

Properties

Once you are selected the program, click OK.