How are they attached to the door and what is the door itself made of?

 

The door itself is made of wood. There are 4 sections on each door. Each section is 9x2 ft. I didn't see nails, so I guess they are glued to the door?

 

How to install your GarageSkins Realwood Overlay System on your existing door. - YouTube
I found this but the door is steel.

 

Interesting! Product is not available at this stage though.

 

Sorry, no experience with it so anything would be guessing.