To import an OBJ 3D model without plugins, use software with native OBJ support (like Blender, SketchUp Free, or Windows 3D Viewer) and select "Import" from the file menu to load your OBJ.
OBJ is widely compatible, so most 3D tools handle it without add-ons—just keep linked MTL (material) files in the same folder as the OBJ to retain textures.
For beginners, Blender (free) or Windows 3D Viewer (pre-installed on Windows) offer a straightforward, no-plugin workflow.