Basically the demo version and full version of a d16 plug-in are same binary file. That allows you, after a purchase, to activate the plug-in (working as demo) to a fully activated one. Don't be supriprised when you see plug-in asking for a key file (black splash window) even if you install the demo; you may ignore it, and click somewhere on GUI outside the black box to continue evaluating demo version and close the popup black window.
Note that black splash window in a demo version, apart from link to the shop and button allowing plug-in activation, contains also some useful information like demo limitations.