I am using MacTeX, but does not appear to come with latex2rtf. latex2rtf does not appear in the available packages, so I have separately downloaded the tar.gz file. Can I install this package using the TeX Live Utility?
latex2rtf is a standalone program and not part of 'tex. You need to install Latex2rtf on your mac like you would any other program.
Once you have installed it and added it to your path, you run latex2rtf from the terminal command line.
You may find it helpful to review the manual page at http://latex2rtf.sourceforge.net/usage.html before trying to use it.
Some time ago, I provided a Mac OS X installer package for latex2rtf on my Dropbox account and posted it to the Mac OS X TeX mailing list:
The package is a few years old, but I don't think latex2rtf development has been very active. It installs to
/usr/local, and you'd have to run it from the Terminal as @AndyClifton has pointed out.
If you want to use the .tar.gz from Sourceforge on the Mac, as I recall you'll need to have installed at least the command-line Xcode tools, edit the Makefile, compile from source, and install using the Terminal. It's not hard, but you need to know what you're doing.