How can I add a program to the context menu of all files?

Here is how you do it with an executable, I would assume it could be done with any program.

Open regedit.exe through the start menu search or run box, and then browse down to the following key:

HKEY_CLASSES_ROOT\ *\shell

Right-click on “shell” and choose to create a new key, calling it “Open with (your program name)”. Create a new key below that one called “command”. Double-click on the (Default) value in the right-hand pane and enter in the following:

"C:\Folder path where the program resides\Program.exe" "%1"

The change should take effect immediately… just right-click on any file and you’ll see the next menu entry.

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Source of Information (sort of)

. [Note: Article-comments report author's method works for Vista; and also XP. - Ed.]

You can also try with this little freeware program:

http://defaultprogramseditor.com/

It just sorted out all the mess for me with .js files. Before that I tried several different ways of adding default handler programs. Highly recommended.

Note that I've got nothing with the developer/publisher of the software. Just a happy new user.

Edit: Oh, just found it's been recommended already: Why can't change the default program to open an extension in Windows 7?