Help > Authoring > Dialog Boxes > Edit Window > Tools Dialog Boxes > Compare File Dialog Box
  
Compare File Dialog Box
You can compare the currently active document with a file saved on disk. If one document is free-form XML, the other must be as well. In the Compare File dialog box, choose the file you want to compare to the currently active document. After you select the file, the Compare window displays changes marked according to the Compare Preferences settings.
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While the Compare command will detect the addition or deletion of graphics and equations, it will not detect changes within a graphic or an equation.