With October 13, 2015 release of Acrobat DC, you can now install Acrobat DC without removing the previous version (X or XI) of Acrobat.
While installing Acrobat DC, the Creative Cloud desktop application or Acrobat installer provides you an option to remove or keep the previous version of Acrobat. By default, the Remove old/previous versions option is selected. If you want to install Acrobat DC without removing the previous version of Acrobat, clear the checkbox.
However, if you have both Acrobat X/XI and DC installed on the same computer, some of the workflows and shared resources or preferences do not work with the previous version of Acrobat. They work fine with Acrobat DC.
All PDF creation workflows are blocked from Acrobat X/XI when Acrobat DC is installed. When you uninstall Acrobat DC, the workflows start working again from Acrobat X/XI.