If you are refering to drawing changes, I use a software called Bluebeam PDF to compare the PDF of the old vs. new revision. You can overlay one PDF on top of the other in different colors and it becomes obvious exactly what was changed on the drawing.
Attached is an example. What is in red was old rev, green is new rev, black is consistent across revisions.
If you move a view, it gets a little messing, but overall, its a really handy tool.
Steve