Do anybody know what is the different between the file format of ACIS, PARASOLID, IGES and STEP? Any website can provide me the information of file format above. I appreciate any suggestive opinions. Thanks.

ACIS is the name of a geometry library from Spatial Corp., which is owned by Dassault Systemes, the CATIA people. An ACIS file, usually called an ACIS .SAT file, contains geometry in their native format. I suggest you try www.spatial.com.

Parasolid is the name of a geometry library from EDS, the Unigraphics people. A Parasolid file, usually called a Parasolid X_T file, contains geometry in their native format. I suggest you try www.parasolid.com.

IGES is an acronym for Initial Graphics Exchange Specification, a standardized file format for exchanging CAD data. The web site www.nist.gov/iges has a lot of information about IGES.

STEP is an acronym for STandard for the Exchange of Product model data, an ISO standard (10303) for exchanging CAD data. It is newer than IGES. This web site is as good as any to begin your search: http://cic.nist.gov/plantstep/stepinfo/step_def.htm

I hope this helps.