C# access shared files on remote windows 10 computer over WAN.

We have a C# application that access (modify, etc) shared files/folder on another windows 10 computer (not windows server) in the same network via UNC. We would like to update this application so it can be installed at home but can still access the shared files/folder using windows network share over WAN. We researched SMB and VPN but need an experienced person to help us.