A recent discussion group post highlighted this issue once more and I thought that it would be a good opportunity to repeat what has been said so many times before.
A user wanted to know whether there is a way to markup DWG files in our Autodesk DWG TrueView application, a question that came up many times before and I am sure will be submitted many times again.
Scott Sheppard took the time to post this detailed reply: "Autodesk does not make a tool to redline DWG files directly. Though you and others have asked for it, we find that most people who send out their DWG
files do not want the people doing the redlining to be able to modify them. If we let you redline the original DWG, when you save your redlines, you would change the DWG. We have a similar situation with Revit (RVT) and Inventor (IPT) files. So to solve this problem for DWG, RVT, and IPT in one fell swoop, we use DWF. You publish a DWF from the DWG. Or you use Vault and let it publish the DWF file automatically. You redline the DWF. You save it and change the DWF. You send the DWF back to the person with AutoCAD. That person loads the DWF into AutoCAD and changes the DWG based on the redlines in the DWF."
This was depicted in an old blog posting (the Autodesk DWF Viewer was still around then):