Opening OBJ files in Autodesk Inventor can be a useful way to incorporate 3D models created in other software into your designs. To open an OBJ file in Inventor, follow these steps:

1. Open Autodesk Inventor: Launch the Inventor software on your computer. If you don't have it installed, you can download it from the Autodesk website.

2. Create a New Part: Once the software is open, create a new part or open an existing assembly where you want to import the OBJ file.

3. Access the 3D Model Workspace: In the ribbon at the top of the screen, click on the '3D Model' workspace to access the tools for importing and working with 3D models.

4. Import the OBJ File: Under the 'Insert' tab, click on 'Import' and select 'Mesh'. Navigate to the location where your OBJ file is saved and choose the file to import. You may need to adjust import settings such as units and orientation to ensure the model is imported correctly.

5. Convert the Mesh to Solid: Once the OBJ file is imported, it will be in mesh format. To work with it as a solid object, you'll need to use the 'Convert to Base Feature' tool to convert the mesh into a solid body.

6. Edit and Modify the Model: Now that the OBJ file is imported and converted, you can use the various modeling tools in Inventor to edit, modify, and incorporate the 3D model into your design as needed.

7. Save Your Work: After making any necessary changes or adjustments to the model, be sure to save your work to preserve the changes made to the imported OBJ file.

By following these steps, you can successfully open and work with OBJ files in Autodesk Inventor for your 3D modeling and design projects. Whether you're collaborating with others who use different 3D modeling software or integrating existing models into your designs, importing OBJ files can expand the capabilities of your Inventor workflow.