AutoCAD is a powerful tool for 3D modeling and design, and it supports a wide range of file formats for importing 3D models. If you need to open an OBJ file in AutoCAD, here's how you can do it.

1. Open AutoCAD: Launch the AutoCAD software on your computer to start the process.

2. Access the Import Function: In the AutoCAD interface, go to the 'Insert' tab and click on the 'Import' button. This will allow you to select the OBJ file you want to open.

3. Select OBJ File: In the import dialog box, navigate to the location of the OBJ file on your computer and select it. Click 'Open' to proceed.

4. Adjust Settings: Depending on the size and complexity of the OBJ file, you may need to adjust import settings such as scale and units. AutoCAD provides options for scaling and unit conversion during the import process to ensure the imported OBJ file is properly sized and aligned with your existing designs.

5. Import OBJ File: After setting the import options, click 'OK' to import the OBJ file into your AutoCAD drawing. The import process may take a few moments, especially for larger files.

6. Review and Edit: Once the OBJ file is imported, you can review and edit it as needed within the AutoCAD environment. You can apply various modeling and design tools to modify the imported 3D model to suit your project requirements.

7. Save the Drawing: After making any necessary modifications, remember to save your AutoCAD drawing to retain the imported OBJ file within your project.

By following these steps, you can open OBJ files in AutoCAD and leverage its powerful 3D modeling capabilities for your design projects. Whether you're working on architectural designs, product prototypes, or engineering models, AutoCAD's support for OBJ files enables seamless integration of 3D assets into your designs.