Opening an OBJ file in Blender is a simple process that allows you to work with 3D models in the popular open-source software. Here's how to do it:

1. Launch Blender and navigate to the 'File' menu at the top left of the screen.

2. Select 'Import' and then choose 'Wavefront (.obj)' from the dropdown menu.

3. Navigate to the location of your OBJ file on your computer and select it to import it into the Blender workspace.

Once the OBJ file is imported, you can manipulate and edit the 3D model using Blender's extensive set of tools and features. You can adjust the materials, textures, and lighting to customize the appearance of the model to fit your project's needs.

If you need to export your work back out as an OBJ file, you can do so by navigating to the 'File' menu again and choosing 'Export' and then 'Wavefront (.obj)'.

By following these simple steps, you can seamlessly work with OBJ files within Blender for all your 3D modeling and rendering needs. Whether you're a seasoned professional or just starting out, Blender's intuitive interface and powerful capabilities make it an excellent choice for 3D design and visualization.

So next time you need to work with an OBJ file in Blender, you can do so with confidence and ease knowing that these simple steps will help you get started on your 3D modeling journey.