In the Mac version of Acrobat DC Adobe has introduced a new folder for storing third-party plug-ins. The Plug-ins folder can be found in Library > Application Support > Adobe > Acrobat > DC (subscription license) or 2015 (perpetual license).
Callas pdfToolbox 7.6 is indeed installed in this new folder. However Enfocus PitStop 13 Pro is still in a folder inside the Acrobat application package like in older versions. It seams that both ways are working. However there is a risk that during an upcoming Acrobat update the plug-ins in the application package will be removed. Enfocus has issued a warning and instructions to manually move the Enfocus plug-ins to the new location.