Hi,
Do you mean that you want to protect all the Office files with password via one Group Policy? If yes, please see the article:
https://technet.microsoft.com/en-us/library/ff657853.aspx
On the other hand, I also recommend you try to use Azure RMS to product your files at once.
https://technet.microsoft.com/en-us/library/jj585026.aspx
https://technet.microsoft.com/en-us/library/jj658941.aspx
Regards,
George Zhao
TechNet Community Support
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