Remote desktop is NOT a secure method of remote access to your server from an outside source. Yes, it's better than others, but it's not considered a secure connection. If you want to protect the connection you need to use encryption first such as via VPN. There are many different ways of setting up a VPN connection depending upon the hardware and software you have available as well as your network setup. If this connection is something that ideally needs to constantly be up instead of just utilized every once in a while to get some random data, then you should look into a site-to-site VPN connection. Again this can be done with software, but most often is done at the hardware level with a VPN capable firewall or router at both office locations. I don't really know very much about your office network, the internet connection type, etc. so I can't make direct recommendations yet, but personally for this sort of thing I have used Sonicwall firewalls as they are very easy to set up and very cost effective as well.