Generally in AutoCAD & NX , the drawing file is store in DWG format. DWG format file is one of the CAD file .
If we create a drawing sheet in NX or AutoCAD, we can save it in DWG format. But there might be some data loss or data inaccuracy if we transfer the dwg file from AutoCAD to NX or vice versa.
Other CAD softwares like Catia, Solidworks, Solid Edge, ProE etc uses different file extensions for drawing.
Catia stores the drawing sheet with extension .Catdrawing
ProE stores the drawing sheet with extension .drw
SolidEdge stores the drawing sheet with extension .dft
Solidworks stores the drawing sheet with extension .eDRW
The CAD drawing files created in a specific CAD software cannot be directly opened in other CAD software. Either we should export it into a neutral file format like AutoCAD drawing or the software should have importing license for the specific file format.