These are demonstration  versions which allow you the full use of the
software for  trial  purposes. They  will work  for a  limited number
of uses, after which if you would like to continue using the software
you should register your copy.This allows you to "try before you buy"
,thus allowing you to make  certain that the software is suitable for
the described  tasks and functions  properly.  Personally I think all
software should be sold on a trial basis,this would reduce the amount
of 'crap' software that is being sold on a no return basis.