There are two possibilities (according to this article):
You turned to Word Perfect shortcuts
Solve this by doing the following in MS Word:
- Select Tools in the main menu
- Select Options from the drop down
- Select the General tab
Some other Microsoft option turned on you
Solve this by doing the following in MS Word and/or in MS Outlook:
- Select Tools in the main menu
- Select Options from the drop down
- Select the Edit tab
- Turn ON the toggle for "typing replaces selection".
Makes my wonder why all those gazillion options are there anyway...