There are a number of reasons for excessive file size, including:

1. Fast Saves: Disable this at on the Save tab of Tools | Options.

2. Preview Picture: Clear the check box on the Summary tab of File |
Properties.

3. Versions (File | Versions): Make sure "Automatically save version on
close" is not turned on.

4. Revisions (Tools | Track Changes):
   Highlight Changes: Make sure "Highlight changes on screen" is turned on
(or that "Final Showing Markup" is displayed).
   Accept/Reject Changes: If "Accept All" or "Reject All" is available then
revisions are present; accept or reject all changes, then turn Track Changes
off.

5. Keep track of formatting (Tools | Options | Edit). This is reportedly a
major cause of file bloat in Word 2002 and above.

6. Embedded True Type fonts (Tools | Options | Save); embedding fonts should
be avoided wherever possible.

7. Embedded linguistic data (Tools | Options | Save).

8. Embedded graphics: When feasible, it is preferable to link the graphics.
That is, when you insert the graphic, click the arrow beside Insert in the
Picture dialog and choose Link to File rather than Insert or Insert and
Link.

9. Embedded objects: These are even worse than ordinary graphics saved with
the document. If you see an { EMBED } code when you press Alt+F9, the
graphic is an OLE object. Unless you need to be able to edit the object in
place, unlink it using Ctrl+Shift+F9.

10. File format: Make sure you are saving as a Word document; in some cases
.rtf (Rich Text Format) files are significantly larger than .doc files.

11. Document corruption: See
http://www.mvps.org/word/FAQs/AppErrors/CorruptDoc.htm.