Use UE4 as a part of a MFC software

I created a serious game with a basic 2D graphic interface.
I need now to add a 3D view (like modern games) in an additionnal window (so there will be 2 windows at least : 1 for current 2D view & 1 for the new 3D view). I could use directely DIRECTX 3D functions but the far better & faster way is to use a game engine.
As my serious game is in C++, I choosed UE4 rather than Unity.

I mean that I would like to integrate the UE4 class in my software and, in a loop, give the focus to a kind of “main” function of UE4 part which will display 3D view in an additionnal window.

But, despite my researchs on the net, I haven’t find a way yet to interface in a single software my serious game & UE4.
Any idea ?

My intention now is to get the UE4 source code to find the a so-called “main” function and add my big software into the UE4 source code. And I will pray that the 2 codes are compatibles …

Thank you very much !!

My english is getting better for I’ve just find that the appropriate word for my issue is “embed”.
There is some topics about that.
I will check and get back here to close or not my topic.