The compare sheets tool in Autodesk Design Review is a great tool for checking for changes in geometry between different issues of a drawing. The tool only works on DWF files however. In my experience most people issue drawings in PDF format which meant the tool couldn't be used.
There is a workaround however. You can convert PDF's to DWF's using the DWF writer printer driver which you can download from the following link:
This will allow you to print to DWF from a number of document formats including PDF. Below is the print dialog box from Adobe Reader.