I've done a lot of editing for a lot of years, and one command we editors know about is Word's Comment feature. Pretty much every version has some iteration of Comments, but few people use them. However, in certain circumstances, it can be extremely useful. In situations where multiple people need to share documents and make revisions, being able to explain your changes or add queries can come in handy.
The beauty of comments is that they are actually hidden from the main body of the Word document. Early versions of Word called them Annotations and you had to view them using a menu command. Now Comments display like a little on-line Post-It note, whenever you move your cursor over the highlighted text.
To add a comment, highlight a range of text. Now choose Insert|Comment. In Word 97 and 2000, the text you highlighted appears in yellow (like it has been highlighted with a highlighting pen). In Word XP, the text appears between two red brackets. In all versions of Word, a separate frame appears at the bottom of the page where you can type your comment. Your initials appear at the left, and you type your peerless prose next to them. (Note that the initials information that appears in the pane can be changed by choosing Tools|Options and clicking the User Information tab.)
After you type in your comment, click the Close button at the top of the comment frame area. Now any time you move your cursor over the highlighted text area, your comments automatically pop up. If you want to see all the comments in the separate pane, choose View|Comments. I've found over the years that if you have a lot of comments (i.e., revisions to revisions and multiple explanations), sometimes it's easier to just leave the Comments pane open while you are reading and work with the comments somewhat like on-screen footnotes.
Because the comments are hidden text, they don't print out unless you specifically tell Word to do so. To print Comments, choose File|Print and change the Print What drop-down box to Comments.