When you use the Compare and Merge feature to compare any two documents, Microsoft Word shows the differences between them as tracked changes (tracked change: A mark that shows where a deletion, insertion, or other editing change has been made in a document.).
Balloons show insertions or deletions, formatting changes, and comments.
Collaborate on documents
If multiple reviewers return changes and comments (comment: A note or annotation that an author or reviewer adds to a document. Microsoft Word displays the comment in a balloon in the margin of the document or in the Reviewing Pane.) in separate copies of the original document, you can merge all their changes into a single document, and then you can review each change from the single document. You can continue to work on a document after you send it for review; Word will show both what you added and what the reviewer changed.
Although it's best for reviewers to work with Track Changes (Tools menu) enabled, Word will detect and show changes even if a reviewer didn't turn this feature on.
Comparing documents side by side
Sometimes viewing multiple users’ changes in one document can be overwhelming, but now you can use a new approach to compare documents. Comparing documents side by side allows you to determine the differences between two documents without having to merge multiple users’ changes into one document. You can scroll through both documents at the same time to identify differences between the two documents.
Use merge commands to specify a baseline document
When you select a document to compare with the document that is already open, you use one of three merge commands to specify which document to use as the basis for the comparison. Differences between the documents are shown as tracked changes in the baseline document.
Changes to the document that is already open (red) are shown as tracked changes in the document you selected in the Compare and Merge Documents
Merge into current document
Changes to the document you selected in the Compare and Merge Documents
dialog box (blue) are shown as tracked changes in the document that is already open.
Merge into new document
Changes in both documents are merged into a new, third document, with differences shown as tracked changes.
Compare with Legal blackline option
When you use the Legal blackline option, Word displays a new, third document in which tracked changes in the baseline document are accepted and changes in the selected document are shown as tracked changes. The documents being compared are not changed.
Note If you want to compare changes from a number of reviewers, do not select this option. Use one of the merge commands instead.