Reduce the size of a 3D drawing file in AutoCAD

Specifically for 3D elements in a drawing: 

1. Select all objects in a drawing and enter the BREP to remove the solid history.
2. Turn off saving solid history by entering SOLIDHIST on the command line and setting it to 0 (zero).

Additional options:

• Export 3D solids to a SAT file using the ACISOUT command.
• Delete all 3D solids and import them again using the ACISIN command.
• If AutoCAD Mechanical is available, use STEPOUT and STEPIN instead (layer and colors are better preserved).

More file size reduction can be done apart from 3D elements