There is documentation on DCC, under the CTCP specification:
http://www.irchelp.org/irchelp/rfc/ctcpspec.html

Specifically, DCC <type> <argument> <address> <port> <size>

In case of DCC SEND, it would be:
DCC SEND <filename> <address> <port> <size>.

The command isn't out of date. By your argument, IRC would be obsolete because RFC 1459 was written in 1993.