It appears Acrobat Reader for Mac has a bug in that it print CMY greys on an HP Laserjet M252dw even though the Print in grayscale box is ticked, and the treat grays as K only grays is selected.
In order to print true K only greys one must revert to the system print dialog, after which it will do so.
I don't know if this happens with other printers, but it needs to be fixed. I'm wasting colour ink printing greyscale unless I go through the process each time.
AdChoices