The documentation you mention is for Octave 3.0 which is a very very old version. All of Control functions, together with Finance and Quaternion, were removed from core Octave with release 3.2. If you see the news for Octave 3.2 (if you have a very recent version, this may be in one of the old news file:
** The Control, Finance and Quaternion functions have been removed.
These functions are now available as separate packages from
http://octave.sourceforge.net/packages.html
and can be reinstalled using the Octave package manager (see the pkg function).
As it is mentioned, you can download the packages from Octave Forge website but depending on your operating system, you may be better off use your package manager.
Finally, the ord2
function does not actually exist in the control package and I'm even unsure that the version you are referring to in Octave 3.0 was even Matlab compatible. However, you can still see its source online right before it was removed.