As found on an Adobe Forum…
To deactivate a PC with Adobe Digital Editions 1.x:
Launch Digital Editions 1.x Enter the key-combination of <CTRL><SHIFT>D (<CMD><SHIFT>D on Mac OS) At the dialog, confirm that you wish to de-activate the machine Quit Digital Editions
To reactivate and authorize the machine using the same or a new Adobe . . . → Read More: How to deactivate Adobe Digital Editions
