If you want to configure Word 2007 to save files in the earlier format by default, do the following:
1. Click the “Office” button in the upper left-hand corner, then select Word Options.
2. On the left-hand column, click on the “Save” to display the the settings for how documents are saved.
3. Click on the pull down menu next to “Save files in this format
4. Select “Word 97-2003 Document (*.doc)”
5. Click → OK to save the change.