How do I disable Notepad++'s "This file has been modified..." message? [duplicate]

Settings -> Preferences -> MISC. tab

In the section that says File Status Auto Detection make sure that Enable is unchecked


Settings → Preferences → Misc. → Uncheck Enable under File Status Auto-Detection

Also, as Jet pointed out, you can also have 'Update silently' checked if you want it to auto-update the file.

Uncheck 'Enable' to disable update detection or check both 'Enable' and 'Update silently' to automatically update once a change is made.