If you are a 3D designer or working in the field of architecture, engineering, or construction, you may come across OBJ (Object) files that you need to open and work with in AutoCAD. Fortunately, AutoCAD provides a straightforward way to import and work with OBJ files. Here's a step-by-step guide to help you with the process:

1. Launch AutoCAD: Start by opening AutoCAD on your computer. If you don't have AutoCAD installed, make sure to download and install it from the official website.

2. Prepare the OBJ file: Locate the OBJ file that you want to open in AutoCAD. If needed, ensure that the OBJ file is saved in a location that is easily accessible.

3. Import the OBJ file: In the AutoCAD interface, navigate to the 'Insert' tab and click on 'Import'. Select the OBJ file from the location where it is saved and click 'Open' to initiate the import process.

4. Adjust the import settings: AutoCAD may prompt you to adjust certain settings related to the OBJ file import, such as scale, insertion point, or rotation. Make sure to review and adjust these settings as per your requirements.

5. Complete the import process: Once you have finalized the import settings, proceed with the import process. AutoCAD will now import the OBJ file into your workspace, allowing you to view and work with the 3D model as needed.

6. Edit and work with the 3D model: With the OBJ file successfully imported, you can now start editing and working with the 3D model within AutoCAD. Use the various tools and features available in AutoCAD to manipulate the 3D model according to your design or project requirements.

7. Export the modified file: After making necessary edits to the OBJ file within AutoCAD, you can also export the modified file in OBJ format or any other compatible format as needed. Navigate to the 'Export' option within AutoCAD to save the modified 3D model.

By following these steps, you can seamlessly open and work with OBJ files in AutoCAD, enabling you to incorporate 3D models into your design projects with ease. Whether you are collaborating with other professionals or working on your individual projects, AutoCAD's compatibility with OBJ files can streamline your 3D modeling workflow in a professional and efficient manner.