failed to install adobe reader dc, "latest version already installed" message

You might want to have a look at this...

Download Adobe Reader and Acrobat Cleaner Tool - Adobe Labs

"The Adobe Reader and Acrobat Cleaner Tool removes a standalone installation of Reader or Acrobat, including any preferences and settings that may be preserved during a standard program uninstall."

I appreciate that you said no Adobe software is on your system but the installation process sounds like it's clearly finding something it doesn't like.

I want to emphasise here that I have no personal experience with this so I am not recommending it one way or another. Just a possible a solution for you to explore.