Has the AutoCAD 2005 drawing file format (DWG) changed from the AutoCAD 2004 file format, as it did between AutoCAD 2002 and AutoCAD 2004?
No, the new features and functionality developed in AutoCAD 2005 maintain DWG and DXF™ file compatibility between the AutoCAD 2004 and AutoCAD 2005 software versions. You can directly and easily share files between different design teams using AutoCAD 2004 and AutoCAD 2005. In addition, AutoCAD 2005 has a built-in SaveAs function to save drawings in AutoCAD 2000/2000i/2002 format.