In Microsoft Word I'm aware of two 'gotchas' where you might leak more than you wish. The first is the one above that JohnInKansas mentioned. The second occurs when the writer, YOU, selects a bunch of text and selects for it the option 'hidden text' which makes the text and the space it occupies vanish. This allows a writer to try alternate versions of a paragraph, a sentence, an expression, without leaving the document. Naturally, if you simply send a WORD document which is being worked on in this way, the alternate material is still part of it; this allows collaborators on a document to work 'together while apart'.

It is a powerful tool, and on occasions, a dangerous thing to forget.

The techniques of doing a cut and paste into a simpler format/ program will do the trick of making sure that nothing more than what's in front of you gets out. For formal documents, making it an image and faxing it makes it much much harder for the document to be altered after it leaves your domain.