Because a fresh Notepad++ & Compare Plugin combo works as expected on all the machines I have access to.

Or you might try to download the portable Notepad++ and unzip it into some other folder (maybe on your desktop) and run that (you have to close/exit all other Notepad++ window(s) first), and see if you can make Ctrl+Alt+C work in that instance even when it doesn’t in your installed version – if it works okay in the portable but not in your installed, then something has set itself up as a Ctrl+Alt+C inside Notepad++ if it doesn’t work in either, then I really think it’s external to Notepad++.

Even though you don’t think anything else is hijacking that keystroke, you might try rebooting in safe mode with fewer applications running, and see if that changes behavior.

Ctrl+Alt+C still runs Compare with no problem. Since you had them, I then then installed JSON Viewer and XML Tools plugins as well and restarted Notepad++. Plugins : ComparePlugin.dll mimeTools.dll NppConverter.dll NppExport.dll Solution 4: Reinstall the Notepad The Notepad might not work if its installation is corrupt. I unzipped a fresh portable v8.3.3, installed Compare plugin 2.0.2, and Ctrl+Alt+C worked out-of-the-box The plugin ran fine, but for some odd reason, the default shortcut wont run the expand abbreviation command (ctrl+alt+enter).

Notepad++ shortcut not working