If you need to identify which program opens a particular file type, you can do that, and a lot more, using the Folder Options functions in Windows Explorer.
To find Folder Options, open Windows Explorer (right-click on Start, select Explore). Then, on its menu bar, select Tools and then Folder Options…
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At this point, we need to select the File Types tab.
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On the File Types tab, we see a large, scrollable box that lists file types. As we scroll down the list, we see various file extensions (such as JPG and DOC) along with a text description of the file type.
Typically, the default program has defined the "File Type" description to be shown, so you’ll see that DOC has a file type "Microsoft Word Document". Of course, if the program doesn’t set that description, Windows will put something there…
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Click on a file type or extension and you’ll see an initial display for that file extension.
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You can open the Open With dialog box by clicking on the Change… button. This lets you change the default program that opens this file extension.
So, if I wanted all .DOC files to open in OpenOffice by default, instead of Microsoft Word as my computer currently is set, I’d change it here.
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