Acrobat DC on the Mac is a 64bit application. This is good for the performance. But this also requires that all third-party plug-ins (e.g. Enfocus PitStop, Callas pdfToolbox, Quite, etc.) are in 64bit. You cannot just move the existing plug-ins from an older Acrobat installation to Acrobat DC. You must get an update of all of your third-party plug-ins. For the most important plug-ins you can find additional information on a german info page from Impressed.
Windows users don’t have to worry about this for now since Adobe did not manage to move the Windows version to 64bit yet. This will happen later (and then you will have the plug-in problem also on Windows…).