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…
At this point, we need to select the File Types tab.
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…
Click on a file type or extension and you’ll see an initial display for that file extension.
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.