Opening a .obj file, a common 3D model file format, can be done using various software programs such as Blender, Autodesk Maya, or Adobe Photoshop. To open a .obj file in Blender, for example, simply launch the software, go to 'File' > 'Import' > 'Wavefront (.obj)' and select the desired .obj file from your computer. In Autodesk Maya, you can open a .obj file by going to 'File' > 'Import' and choosing the .obj file. Once opened, you can explore and manipulate the 3D model using the features provided by the software. Understanding how to open and work with .obj files is essential for anyone involved in 3D design and modeling.