How can I edit encrypted files in Microsoft Office Apps?

To edit Office documents with Microsoft Office, you must allow Microsoft Apps access to all files. To do this, proceed as follows:

Open an installed Microsoft Office app (Word, Excel, PowerPoint or “Office”)
Navigate to the ‘Folder’ icon at the bottom of the screen. (In the ‘Office’ app, the icon is in the upper-right corner)
Select “Open” in the menu bar and click on “This device”
If the required authorization has not yet been granted, a dialog will appear that takes you to “Settings”
Enable “Allow access to manage all files” (the text may be slightly different depending on the Android version)
You can now close the Microsoft Office app
Repeat the process for all Microsoft Office apps you need