User Configuration > Administrative Templates > Microsoft Office 2016 > Security Settings > Trust Center > Application Guard
User
HKCU\software\policies\microsoft\office\16.0\common\security\applicationguard
This policy setting allows you to control whether users can remove Application Guard protection and open a document with full trust in Office. If you enable this policy setting, users can continue to work with Office documents in Application Guard, however, they cannot remove protection and open a document outside Application Guard. If you disable or do not configure this policy settings, Office will by default allow users to remove protection and open a document with full trust. Note: This policy setting only applies to Microsoft 365 Apps for enterprise.