The Compare feature in Word 2013 analyzes two documents and generates a report on their differences. Comparing works similarly to tracking changes, in that you can accept or reject each alteration. Unlike tracking changes, you don't need to turn on compare ahead of time: As long as you have two separate copies of a file, you can compare them, even if multiple authors have made changes.
Open Word, switch to the "Review" tab, click the "Compare" button and choose "Compare" from the drop-down menu. You don't need to open either document prior to this point -- click "Compare" directly from a new document.
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Click each "Browse" icon to locate the original and revised documents on your computer. Optionally, enter an editor's name in the right "Label changes with" box to mark the revisions by name. Press "More" to open the comparing options.
Uncheck any types of differences you want ignored. By default, comparing documents generates a new file that shows the differences to avoid modifying either existing file. If you'd rather show the changes in one of the two existing files, select either "Original Document" or "Revised Document." Press "OK" to create the comparison.
Review the changes line by line in the left-hand Revisions pane. On the right side of the window, you can see both versions of the document. In the center, Word marks each paragraph containing changes with a red line. Click this line to display specific revisions.
Select a revision and click "Accept" or "Reject" in the Changes section of the Review tab to determine which alterations to retain. If you place your cursor over a revised section of text, Word displays the time and date of the change.
Save the document after accepting or rejecting all items in the Revisions list. Unless you chose to show changes in the original or revised document, Word saves the edited document as a new, third version of the file.
To compare two files visually without having Word analyze their differences, open both at the same time, switch to the "View" tab and click "View Side by Side" in the Window section. You can also press "Arrange All" to place the documents atop one another. Zoom out with the slider in the lower-right corner if necessary to fit the document contents in the small window.
Enable "Synchronous Scrolling" on the View tab to scroll both documents whenever you move up or down in either window.
Choosing to display the changes in one of the existing documents overwrites that document when you save after accepting or rejecting changes. In most cases, it's best to leave the "Show changes in" setting on the default "New Document" to preserve multiple versions as backups.
If either existing document already has tracked changes, Word prompts you to accept them before generating a comparison, as the program can't store two sets of changes for one document.