While themes are a gimme for working in PowerPoint, they don’t appear to be as useful in Word as they don’t seem to do much to format the document if you’re not using diagrams or shapes. However the problem isn’t quite this simple. Themes in Word won’t apply to the text in the document if you don’t have a style in place. Use the Home tab to view the Styles option and click Change Styles and select a Style Set. Now, when you choose the Theme, the styles available change.
All of a sudden, themes make a little more sense in Word 2007.