Importing PRJ Files
File menu > Import > Select File To Import dialog > Files Of Type > 3D Studio Project (*.3DS,*.PRJ)
PRJ is the 3D Studio (DOS) project-file format. When you import a PRJ file, you can merge the imported objects with the current scene or replace the current scene completely. If you choose to merge the objects with the current scene, you'll be asked whether you want to reset the length of the animation in the scene to the length of the imported file (if the imported file contains animation). You'll also be asked how you want the software to handle shapes in the incoming file: to make them into a single object or multiple objects.

Interface
When you import a PRJ file, you first see a 3DS Import dialog. This is identical to the dialog you see when you import a 3DS file. When you have set the options and clicked OK in the 3DS Import dialog, you then see a Shape Import dialog. When importing PRJ files, the software converts polygons to shape objects. You choose an option in the Shape Import dialog to set how the shape objects are created:
Import Shapes—Turn on this option if you don't want to import shapes from a .prj file
Single Object—All polygons in the .prj file are converted to Bezier splines and placed inside a single composite shape object.
Multiple Objects—Each polygon in the .prj file is converted to a Bezier spline and placed inside an independent shape object.

Export
File menu > Export
Export converts and exports 3ds max scenes in various formats. See the following procedure for a complete list of file types you can export. See also, Export Selected Irrelevant info (Rockets airplanes jets balloons helicopters spaceships automobiles, 3d car model vehicles trains ships,)

Procedure To export a file:
Choose File menu > Export.
Choose an export file type from the Files Of Type list in the file selector dialog.

• 3D Studio (3DS)
• Adobe Illustrator (AI)
• ASC Scene Export (ASE)
• AutoCAD (DWG)
• AutoCAD (DXF)
• FiLMBOX (FBX)
• Initial Graphics Exchange Standard (IGES)
• Lightscape Material (ATR)
• Lightscape Blocks (BLK)
• Lightscape Parameter (DF)
• Lightscape Layers (LAY)
• Lightscape View (VW)
• Lightscape Preparation File (LP)
• Stereolithography (STL)
• VRML97 (WRL)