Oops I Set Outlook to Use Notepad to Open that File and It Displays the Whole File on One Line

Who hasn't done that before?

So, you want to change the Application associated with that file type.

My experience with the Windows 10 Settings utility wasn't good. So, here's what I recommend :

1. Launch the Settings utility.
2. In the Find a Setting field, put in Control Panel and hit Enter.
3. Control Panel launches, but has jumped the gun, so you have to use the navigation bar on top to go back to Control Panel from "All Control Panel Settings" (if you're dumb like me :)
4. Now, click on Programs
5. Now, click on Default Programs
6. Then, click on "Associate a file type or protocol with a program" -- can take a few seconds to load
7. Scroll down till you find your extension, select it and then click the Change Program button.