The most straight forward way I have found to do this has been to go to:
get.adobe.com/reader (or /flashplayer)
and get the most recent version for the OS you are trying to install with. (If you are getting this for another platform that what you are on (in my case linux to OSX) be sure to click on the link that asks about another language or OS)
In this case we are dealing with OSX and more specifically (at the time of this response) AdbeRdr11003_en_US.dmg
First mount it with:
hdiutil mount /Path/to/AdbeRdr11003_en_US.dmg
OSX will mount it to exactly:
In the above directory, there is a .pkg file. To install it (as sudo or root):
installer -pkg Adobe\ Reader\ XI\ Installer.pkg -target /
(to explain the above just in case people are new to this, installer is the program, pkg is the option for installing pkg files, then /Path/to/Adobe\ reader.pkg (the "\" is the escape character to allow for spaces in command line) target is the option that tell you what base path this update to install to (in this case it is the base root directory) it is smart enough to figure out where adobe reader is)
You will get some output like this:
installer: Package name is Adobe Reader XI (11.0.03)
installer: Upgrading at base path /
installer: The upgrade was successful.
If you see the above it installed correctly.
To unmount it run:
hdiutil unmount /Volumes/AdbeRdr11003_en_US
I should also mention, that if it should fail it is because there is an old version of adobe reader that needs to be uninstalled first. To do this (using sudo or root):
rm -rf /Applications/Adobe\ Reader.app/
This will remove the old version of reader and is then ready to install the update (or in this case) the reinstall.
Tested 2013-06-18 07:50 EDT