When you collaborate on a document, you can turn on the Track Changes feature so that the revisions you make to the document are recorded without the original text being lost.
You can insert comments in a document to ask questions or explain suggested edits. In the document, Word inserts colored brackets around commented text and displays the comment in a balloon in the margin of the document.
You can protect a document with a password so that only certain people can open it.
You can restrict who can make editing and formatting changes to a document. You can also specify that only comments can be inserted in the document, or you can require that changes be made using change tracking.
You can send a document for review via e-mail, and then when you receive the reviewed versions, you can merge them so that all the changes are recorded in one document.