if you install openvpn on windows server , it is very convenience to have everything to make it work so let making to have access local file .
you need to install routingandremoteaccess service and DNS server and WINS server after that open routingandremoteaccess and config with NAT type as picture
on the main internet card you click and chose as public and NAT
continuce chose openvpn network card and chose private as picture
just open WINS server to make sure everything start and you can access local access now
when you install all of them it will perform NAT and netbios over ip so from client openvpn you can type name to access local resource, if you like you can run multi instance openvpn so it can use all CPU core it mean faster connection to all client and if there are many clients connect to it it can service very well