Importing UDK elements into UE4

I have a friend who is looking to work on some assets for a game we are creating in UE4 and I was wondering as to how we could import architectural objects and the likes he makes into the UE4 Engine? Or if that is even possible?

I think in the Tools section there’s some stuff a guy create to help move UDK assets to UE4

Alternately, you can still import your source files to UE4.

Will importing the source files allow me to then add the UDK content ontop of content I already have?

Here are some of the tools which darthviper107 mentioned:

You can always add more content to your project no matter if you want to have them in the UE4 or UDK