How to transfer data from one computer to another if they are on different networks - c#?

Question

Computer networks

Let me have two computers:
- one in the local network with a "white" ip 12.34.56.78 and has a "gray" ip 192.168.0.2
- the other in the local network with a "white" ip 78.56.34.12 and has a "gray" ip 192.168. 0.3
The task is to transfer an array of bytes from one computer to another using c#. I found examples of TCP / UDP chats only those that work inside the local network and no more.
PS I read about port forwarding that you need to configure the router itself. Then another question follows from this - why, when downloading something using a torrent, you do not need to configure the router? The transfer of the file itself happens peer-to-peer.

Answer 1

On one of the routers you do port forwarding.
Either router settings, or upnp, nat-pmp, etc.
In torrents and others like them, automatic port forwarding protocols have been built in for a very long time