When you choose Insert |
Date and Time from the menu (or click Date and Time
in the Text panel of Word 2007's Insert ribbon), you get a Date and Time dialog that lets you choose the desired format. There's a tricky little box at the bottom labeled Update automatically. If you check that box, Word inserts a date field rather than a static date. This field updates to the current date every time you open the document. When you click on such a date it gets a gray highlight—that's a clue you're looking at a field.
Going forward, be sure that box is not checked when you want to insert a static date. For your old documents, you'll have to delete the date field and replace it with the date that should be there. Not sure of the correct date? It's probably the date that the document was created or last saved. In Word 2003, choose Properties from the File menu to find the Created date.