netDxf is a .net library programmed in C# to read and write AutoCAD dxf files. It supports AutoCad2000, AutoCad2004, AutoCad2007, AutoCad2010 and AutoCad2013 dxf database versions, in both text and binary format.
dxflib is an open source C++ library mainly for parsing DXFTM files. QCAD, CAM Expert and vec2web all use dxflib to import DXF files. dxflib can also write DXF files, but you need to have good knowledge of the DXF format to produce valid output
