Your best option for converting files saved in Autodesk Design Web Format (.dwf) would be to use AutoCAD itself, from which these files were probably exported. But, it is true that .dwf files are typically generated for publishing reasons and it may not always be possible to convert them to anything else (including IGES format). The most reliable way would be to use the original CAD source.
Open DWF file Open IGS fileA 3D CAD translation software