Please see Ron's comment to the question. As these are files, it could be some available service, first of all, FTP.
If you really want to write your own application (who knows? maybe you need to have some other features?), you can do it on several different levels of networking, from raw sockets to classical .NET remoting or WCF. Please see my short overview of some of those levels in my past answers:
how i can send byte[] to other pc[
^],
Communication b/w two Windows applications on LAN.[
^].
—SA