First, some backrgound context as follows: I have a Windows Server 2008 running for my company. It contains an ERP, which is accessible by other computers/clients on LAN. During the client setup, the only thing the client softare needs is, access to the shared folders on the Server. After the setup, the software on the clients just uses these shared folders for its communication with the ERP on the server. I believe the ERP server-client communications are unsecure, but I guess it's fine since it is only used within the LAN.
Now, I would like do the exact same thing as above, but for a client that is on the internet, hundreds of miles away. That is, the client needs to access the shared folders, just like the clients on LAN. Additionally, is there any way to make it secure, without using a VPN (because the VPNs in this area are usually not allowed by the local regulations)?
I thought of port-forwarding, but I realized I don't know exactly which ports windows uses for sharing folders, and quite possibly, the port-forwarding option might be insecure.
Thank you for taking the time to read & helping me out!