Is it possible to send file via FTP protocol from PC to PC on the Internet? If it is how I can do that ?
Yes, if the destination PC is running an FTP server and if you know its IP address. But this is hardly a programming question.
The only thing not included in the guide would be the firewall setup. Windows XP SP2 and up (or SP3... I can't remember), Windows Vista and Windows 7 all have built in firewalls enabled by default. In addition to the client firewalls, you'll have to set up the router's firewall so that it allows the client PC to connect to the PC that's running the FTP server software.
Overall, this is a real hassle. Have you considered using a common Dropbox or Drop.io account? Neither requires much setup and the transactions are encrypted to boot (at least they are with dropbox, not sure about drop.io) as opposed to when you're doing things in FTP everything sent is sent in plaintext (meaning, your username and password that you use for the FTP account).