3d models not working

I'm kind of new to HitFilm.  I was wondering how to use 3d models in HitFilm so I watched this tutorial:
I went into the video's description and clicked on the link to download a Helicopter model.  When I tried downloading it, it came out as a .7z , and wouldn't open.  I want it to come out as a .obj or a .3ds.  I'm not sure why its not working.  Please help :D
btw I'm using an iMac.