Hi mitay-walle,
Are you referring to something in UnrealScript for UDK? If so, you will need to ask on the UDK forums, as this site is specifically for Unreal Engine 4.
If you are asking if you can use something from Unreal Engine 4 in UDK, then no. The engines are completely different, with the primary difference in relation to code being the use of C++ in UE4 and UnrealScript in UDK.