This problem was confusing for me at first because I thought you had to fix this issue in Outlook. You don’t; you fix this in Word. You may see the following error:

This error occurs when you open a Microsoft Office file type blocked by File Block settings in the Trust Center.

Example: “I want to turn on my out of office but it won’t let me.”

Resolution: Open Word and click on File > Help > Options. Then go to Trust Center > Trust Center Settings > File Block Settings. Click on Restore Defaults, and click OK to the open windows. Close Word and try editing the signature again.