When there are lots of extensions and different programs to open it, we might want some extensions to be opened with a particular program. We can set up the default programs for each type of extensions in Windows 7. To set up a program to be default for a particular extension, open control panel and select the option Default programs from the all control panel items.
In the default programs, you have two options, first one is to set a program default for particular file extensions and second is to make an extension to open with a particular program. In the first option, you can see all the installed programs and when we select a particular program, it shows whether the program is default for the type of extensions it is supposed to open. Here you can set the program default for all programs which it can open and also chose selected extensions to open with this program.
In the second option, all the file extensions are displayed and the current default program associated with the extensions.
If you want to change the program, click change program and select the program you wish to associate to the file extension.