Opening OBJ files for 3D modeling and design can be done using a variety of software programs. One of the most common methods is to use 3D modeling software such as Blender, Maya, or 3ds Max. These programs allow you to import OBJ files and view them in a 3D environment, making it easy to manipulate and edit the objects within the file. Another option is to use a dedicated OBJ file viewer, which provides a simple way to open and view OBJ files without the need for complex 3D modeling software. One popular OBJ file viewer is MeshLab, which is a free, open-source program that allows you to view, edit, and convert OBJ files. To open an OBJ file with MeshLab, simply download and install the program, then open the file through the file menu or by dragging and dropping it into the program window. Additionally, some 3D printing software also support OBJ file import, so if you're looking to 3D print an object from an OBJ file, check if your 3D printing software supports OBJ file import. Overall, opening OBJ files for 3D modeling, design, or 3D printing purposes can be accomplished using various software programs and viewers, providing you with the tools to work with 3D objects in a digital environment.