The following information provides some insight in how the different file format structures work.

Name	Extension	Polygon Import	Polygon Export	NURBS Import	NURBS Export
Wire format (Autodesk)	.wire
C4 format (Standard CAD)IGES subset format.	.c4x
STEP format ISO standard industrial automation systems product data representation and exchange format.	.stp.step
Autodesk Inventor format C4 format Translations require Autodesk Inventor or Autodesk Inventor Viewer to be installed.	.iv
PTC Granite format (Windows Only)(PRO/ENGNINEER or any Granite based system)	.g.prt (Pro/E part file).asm (Pro/E assembly file)
JAMAIS format (Standard CAD)Japan Automobile Association IGES subset.	.igs
VDAIS format (Standard CAD)Verband des Automobilindustrie - IGES Subset.	.iges
VDAFS format  (Standard CAD)Verband des Automobilindustrie - FlachenSchnittstelle.	.vda
DES format (Standard CAD)Data Exchange Standard. Contains polylines. Requires less space than equivalent IGES files.	.des
DWG format (AutoDesk)Drawing Format.	.dwg
DXF format (AutoDesk)Drawing Exchange Format.	.dxf
SLC format (Solid Imaging)3D Systems Slice format.	.slc
STL Format (Solid Imaging)3D Systems SLA file format. Used to send data to a stereo lithography machine. Binary and ASCII format.	.stl	(imports as a mesh)			(uses a shell to convert to STL)
CAI format for CATIA V4 files (CATIA)CATIA Alias Inter operate ability file format.	.cai
CATIA V5 format	.CATPart.CATProduct
OBJ format (Autodesk)	.obj
Encapsulated Postscript format (Standard)	.eps
VRML format Virtual Reality Modeling Language(3D Object Oriented Toolkit)
Pro/ENGINEER Render file format	.slp
IGES format (SolidDesigner)Initial Graphics Exchange.	.iges, .igs
OpenInventor format (IRIX and Windows)	.iv
Illustrator format	.ai
NX par and assembly format	.prt