User Configuration > Administrative Templates > Microsoft Office 2016 > Miscellaneous
User
HKCU\software\policies\microsoft\office\16.0\common\general
This policy setting turns on and off the ability of users to select an Office background. If you enable this policy setting, users won’t see the Office Backgrounds setting in either the Account place or the Options dialog. They also won’t have an Office Background applied to the upper right of their Office applications. If you disable or don’t configure this policy setting, users will see the Office Backgrounds setting in the Account place and in the Options dialog, and they will have an Office Background applied to the upper right of their Office applications.