Follow these steps to get rid of this error:
- Open Microsoft Word
- Go to File -> Options -> Trust Center.
- Now click on Trust Center Settings.
- Click Protected View in the left pane.
- Now uncheck the box: Enable Protected View for Outlook attachments.
- Click OK to save changes in Trust Center window.
- Click OK in Word Options.
Now close your Microsoft Word document and attempt to open an email with a Word document attachment.
You can repeat all the above steps in Microsoft Excel as well