This policy setting lets you control whether Windows Store apps can open files using the default desktop app for a file type. ...

This policy setting lets you control whether Windows Store apps can open files using the default desktop app for a file type. Because desktop apps run at a higher integrity level than Windows Store apps, there is a risk that a Windows Store app might compromise the system by opening a file in the default desktop app for a file type.

If you enable this policy setting, Windows Store apps cannot open files in the default desktop app for a file type; they can open files only in other Windows Store apps.

If you disable or do not configure this policy setting, Windows Store apps can open files in the default desktop app for a file type.