Cause 1
 
You either downloaded the file from the internet or opened it from an email. By default, Word displays the file in protected view.
 
Solution 1
  1. Click Enable Editing in the yellow bar at the top of Word.
  2. Close Word.
  3. Open the Word document again.
 
Cause 2
The file is saved on a network drive or server.
 
Solution 2
 
Add the file path to the list of trusted locations in Word's Trust Center:
File > Options > Trust Center > Trust Center Settings > Trusted Locations > Add new location