In Word 2007, Office button - Word Options - Trust Center - Trust Center
Settings - Privacy Options, remove the check next to "Make hidden markup
visible when opening or saving".
This will affect ONLY your own settings. It will not affect how things open
on somebody else's computer. It cannot be set on a per-document basis.
Now that I've told you how to do it, let me advise you NOT to use disable
this option. If you do, then you run the risk of sending out documents that
still contain changes. This is under Privacy Options because sending out
documents that still contain tracked changes and comments can be a
tremendous source of embarrassment.
So... suppress this option at your own peril. It's turned on by default for
a good reason.
If you need to send out a document without changes showing, then either save
a copy with all changes accepted, or save a copy as a .pdf.