I went and created a new normal world without any modifications and tested this out. I enabled cheats and typed /summon minecraft:ender_dragon
It spawned the ender dragon with all his sounds and roaring but it was just flapping in the air, not moving a inch!
Swords and arrows does no damage. I tried blowing it up with a lot of TNT..... no effect.
I used version 1.11.2
in minecraft 1.9 summoning ender dragon not work anymore
bigbossgerhard you can summon the ender dragon in 1.8