For years draughtsmen and women have been creating markups on hard copies. Autodesk has introduced a more workflow that keeps everything paperless.
Using your AutoCAD you export to DWF (x) and open the file in Autodesk Design Review (ADR). Once in ADR you can do all your markups. Now this is where the magic happens. In AutoCAD open your markup manager. Through the markup manager you can open the DWF that has been edited and be able to see the reviews.
This video illustrates the worflow.