If you're a Mac user and need to edit .obj files for 3D modeling and design, you're in luck. There are several applications available that make it easy to edit .obj files on a Mac. Here's a simple guide to get you started.

1. Use a 3D Modeling Software: There are several 3D modeling software options available for Mac, such as Blender, Maya, and Cinema 4D, which support the editing of .obj files. These applications make it easy to import, edit, and export .obj files with a user-friendly interface.

2. Import the .obj File: Once you have a 3D modeling software installed, import your .obj file into the program. This can usually be done by selecting 'File' and then 'Import' from the menu, and selecting the .obj file from your computer.

3. Edit the .obj File: Once the .obj file is imported, you can start making edits to the 3D model. This could include changing the shape, size, texture, or color of the object, depending on your specific design needs.

4. Save or Export the Edited File: Once you're satisfied with the edits, you can save or export the file in .obj format. This will allow you to use the edited 3D model in other applications or projects.

5. Use a Text Editor: If you prefer to edit the .obj file manually, you can use a text editor like TextEdit or Sublime Text. Simply open the .obj file in the text editor and make the necessary changes to the code. This method is more advanced and requires a good understanding of the .obj file format.

6. Validate the .obj File: After making edits to the .obj file, it's important to validate the file to ensure there are no errors. There are online .obj file validators available that can help you identify and fix any potential issues with the file.

By following these simple steps, you can easily edit .obj files on your Mac for 3D modeling and design purposes. Whether you prefer using 3D modeling software or manually editing the file with a text editor, there are plenty of options available to suit your needs.