If you’re having trouble opening a file that you know is there, but can’t seem to find the right program to open it with, your first step may be to check the file association. This is a set of rules that tell Windows which program should be used to open a particular type of file. To check your file association, open the Start menu and click “Control Panel.” Under “Appearance and Personalization,” click “File Types.” In the list on the left, under “File types associated with programs,” double-click on the name of the program you’re trying to open the file with and then look in the list on the right for the type of file that it opens. If you don’t see an entry for that type of file, it means that Windows hasn’t assigned it an association yet. To change your default program for opening files of a certain type, go back to Control Panel and under “File types,” click on “Default programs.” In this window, you’ll see a list of all programs installed on your computer that are capable of opening files of that type. Click on the name of the program you want to become your default program for opening files of that type and then OK out of this window. ..
The option to delete a file association is conspicuously absent from file associations user interface in Windows 7, so how can you delete file associations you no longer want? Read on as we explore how to remove a default file association.
Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites.
The Question
SuperUser reader Christothes writes:
While the tool for doing so definitely moved, certainly the option to remove a file association hasn’t vanished completely.
The Answer
SuperUser contributor Peter Mortensen offers the following solution:
It takes a little longer to root through the registry in search of the file association key than to use the old file association user interface, but it gets the job done.
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\FileExts
Deleting the sub-key with the same name as the extension you want to un-associate will delete the default program association. You’ll have to kill and restart explorer.exe for this to take effect.
You may also need to remove the same sub key from HKEY_CLASSES_ROOT as well.
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