I have often been asked how does one share an Autodesk Civil 3D 2005 (C3D) drawing with someone with "basic" AutoCAD.
There are three most common results possible:
1. Share the dwg as is. It can only be opened in AutoCAD 2004 or 2005. They will see the C3D objects as Proxy Graphics
2. Share the dwg as is with someone who has the Civil 3D Object Enabler installed. It can only be opened in AutoCAD 2004 or 2005. They will see the "objects" as they are and can get properties and information from them.
3. I can use one of the two "Export To AutoCAD..." commands. These commands create a new drawing and explode all of the Civil 3D Objects into Basic AutoCAD entities per their appearance at that moment in the view in which the command is run. The commands are "EXPORTTOAUTOCAD2004" and "EXPORTTOAUTOCAD2000". These commands can also be found under the "File" pulldown > "Export to AutoCAD" flyout. The ...2000 version creates a 2000 format dwg which can be opened in AutoCAD's 2000, 2000i, 2002, as well as 2004 & 2005.