Good question! To do that I think you can do the following:

- open Indexing Options (get to there from the Start Menu, or from Control Panel)

- click on Advanced

- go to the File Types tab

- find doc, docx, or whatever in the list

- change from "Index Properties and File Contents" to "Index Properties Only"

Honestly I haven't tried this so I can't vouch for it, but it seems to be the official way to go.