This is the result of an AutoCorrect entry that is present by default in
Word. I'm not sure how you could have deleted it inadvertently, so you might
want to check and make sure that you have AutoCorrect enabled (Tools |
AutoCorrect Options: Replace text as you type). If that option is enabled
and you see other AutoCorrect entries listed (indicating that your
AutoCorrect data file is intact), then you can replace this AutoText entry,
as follows:
1. In your document, use Insert | Symbol to insert character 74 from the
Wingdings font.
2. Select the character and open Tools | AutoCorrect Options. You should see
your smiley face in the "With" box.
3. Type
in the "Replace" box.
4. Make sure that the "Formatted text" radio button is selected.
5. Click Add, then OK.