Is it possible to open 3d obj files without a plugin like video copilot or is there no way around it?
Not possible. Sorry. If you have an obj that you have to get into a shot you're going to have to bring into a 3d application (like C4D Lite) do all the animation in the 3D app then bring into AE via traditional rendering and compositing (or cineware if you're using C4D)
What the man said - AE has no native 3D capabilities to deal with geometry/ meshes.