Anytime you make additions or deletions in another's Word 2007 document, you can turn the track changes feature so they can see easily identify the changes you've made and later to accept those changes or revert back. In addition it's also helpful to be able to insert comments next to those marked in red changes you've made, letting them know your reason for changing certain parts of their document, or simply noting to them your concerns. To setup a document you received from say a coworker to track changes you'll be making you'll have to turn it on. To do so go to the Review Tab, to Tracking group and click Track Changes button or its arrow to Track Changes.

Purchase the training video and you can see this in action for yourself!