User Configuration > Administrative Templates > Microsoft Office 2016 > Security Settings > Trust Center > Protected View
User
HKCU\software\policies\microsoft\office\16.0\common\security\protectedview\locations\location6
This policy setting allows you to specify a location containing files that should always open in Protected View. If you enable this policy setting, you can specify a location containing files that always open in Protected View. If you check the "Allow sub folders" option, sub folders will also be included. If you disable or do not configure this policy setting, only the "Downloaded Program Files" and "Temporary Internet Files" folders will be considered unsafe locations.