CAD Files Extensions - What are cad files and how do I open a cad file?

What are cad files and how do I open a cad file?

File Type Category File Format
.123dx CAD Files 123D Design Model File
.catpart CAD Files CATIA V5 Part File
.cdw CAD Files KOMPAS Document
.cgr CAD Files CATIA Graphical Representation File
.dgk CAD Files Delcam 3D Model File
.dgn CAD Files MicroStation Design File
.drwdot CAD Files SolidWorks Drawing Template
.dwfx CAD Files Design Web Format XPS File
.dwg CAD Files AutoCAD Drawing Database File
.dxf CAD Files Drawing Exchange Format File
.easm CAD Files eDrawings Assembly File
.fmz CAD Files Form•Z Project File
.fpd CAD Files Front Panel Designer Project
.fzz CAD Files Fritzing Shareable Project File
.igs CAD Files IGES Drawing File
.ipt CAD Files Inventor Part File
.jam CAD Files Jam STAPL File
.lcf CAD Files ArchiCAD Library Container File
.ldt CAD Files Eulumdat Formatted Luminaire Data File
.lyc CAD Files bestIMAGE Compressed Design File
.nc CAD Files Mastercam Numerical Control File
.pipe CAD Files PIPE-FLO Project File
.pla CAD Files ArchiCAD Project Archive
.pln CAD Files ArchiCAD Project File
.scad CAD Files OpenSCAD Script
.shx CAD Files AutoCAD Compiled Shape File
.stl CAD Files Stereolithography File
.vtf CAD Files Valve Texture File
.vwx CAD Files Vectorworks Design File