Free Tools from Autodesk

How about a free DWG viewer that you can plot with as well as convert down to a version of AutoCAD lower than a file you cannot open with your older version:
http://www.autodesk.com/dwgtrueview

How about a free DWG/DXF/DWF/DGN/JT file format viewer that will allow a user to electronically comment on and/or measure content in those files and return to the file originator for an update:
http://www.autodesk.com/designreview ◦

Free Tools from Autodesk