Working in a map document (.mxd) errors can be created from a variety of interactions between the .mxd file and the data, resulting in a decrease in performance or possible corruption. Compacting reduces map size, avoids errors and improves performance.
Follow the steps below:
Open the problem .mxd file in ArcMap.
Go to the File menu; select Save as.
Select the preferred location.
Change the name of the map document.
Click Save and close ArcMap.
To verify the compaction, open Windows Explorer and navigate to the location of the two .mxd files. Compare sizes between the original file and the newly named file.