This functionality was removed in Update 33.
In the SmartPlant Foundation Desktop Client, you can compare non-published third-party files side-by-side using the Compare Files window. For help using the window's controls, see the viewer's Help file.
The viewer's Help file might refer to functionality that is not available to you.
Search for two third-party files, and then select the two files.
Right-click the selected files, and click Compare Files.
You can drag another file from the list view onto the right or left side of the Compare Files window to view a different file.