User Configuration > Administrative Templates > Microsoft Word 2016 > Word Options > Security > Trust Center > Protected View
User
HKCU\software\policies\microsoft\office\16.0\word\security\protectedview
This policy setting lets you determine if files on local Intranet UNC file shares open in Protected View. If you enable this policy setting, files on local Intranet UNC file shares open in Protected View if their UNC paths appear to be within the internet zone. If you disable or do not configure this policy setting, files on Intranet UNC file shares do not open in Protected View if their UNC paths appear to be within the internet zone.