Hi. Im currently using Unity3d as game engine, but planning to change to UDK. I have few questions.
Is Unreal Engine just an extension to UDK? So can i learn and use UDK, and then subscribe to Unreal Engine? If yes, then can i continue my game, that i made in UDK, after i subscribed to Unreal Engine? Is the code and the editor are the same in both of them?
I know these are silly questions, but i could not find any information, about these two.Im really considering to start learning udk/u4, cuz unity really limits me. Thanks in advance.
UDK → the free version of the UE3. With UDK experience it will be easier for you to start with the UE4, but I personally would directly go with the newer engine, because you cant port your stuff from UDK into the UE4! (just meshes and textures can be ported). 
Many stuff works the same in the UE4, but there are also many differences → e.g
- UE4 = C++; UDK = Unreal Script
- UE4 = Blueprints; UDK = Kismet (it’s comparable with the level bp from the UE4)
- they have a different UI
- …
Thanks alot. I think im gonna learn UDK for few weeks, then go for full engine
Directly start with the UE4. Many stuff that you will learn in UDK will be wasted time 
Thx,for advice