In Autodesk Inventor 2013, you can import obj files to incorporate 3D models into your design projects. To do this, follow these steps:

1. Launch Autodesk Inventor 2013 and open the assembly file or project in which you want to import the obj file.

2. Go to the 'File' menu and select 'Open.' Navigate to the location of the obj file on your computer and select it.

3. In the dialog box that appears, make sure to select 'OBJ' as the file type, and then click 'Open' to import the obj file into your project.

4. Once imported, you can manipulate and work with the obj file as you would with any other 3D model in Autodesk Inventor 2013.

Keep in mind that while importing obj files, it's essential to ensure that the file is compatible with Autodesk Inventor 2013's requirements. If the obj file contains complex textures or materials, it may require additional adjustments or simplification to work seamlessly within the software.

By following these steps, you can easily integrate obj files into your Inventor 2013 projects and take advantage of the diverse modeling capabilities offered by this software.