You can do it through a sockets program, but the easy way is to FTP the file over to the AS/400, and process that with an RPG program. The destination file can either be a flat file or a DDS-defined file.
If the file on the server has several different formats (like a bank ACH file), I have logicals over the flat file which define the fields and select only that format. If all you need to do is read the file, then that should work.
"When once you have tasted flight, you will forever walk the Earth with your eyes turned skyward, for here you have been, and there you will always long to return."
--Leonardo da Vinci