Retrieving back buffer

I am new user of unreal and have very little knowledge of unreal. I have a query… I have a standalone application and want to use unreal engine. so how can i retrieve the back buffer of unreal engine in my application?

For what usecase and which Backbuffer do you need ?

Suppose i am rendering some graphics on unreal engine and want to use rendertraget(baackbuffer) of that rendered graphics in my application… How is it possible? Can i transfer the rendertarget to my application? I am using Dx9 in my application.

You mean a realtime stream of the render output of Unreal ?
If so you can either use Pixelstreaming or a new feature from 4.26 called “Inter-Process GPU Texture Sharing”.