Welcome to CiteHR.com !!!
Yes there is a difference between Original and Duplicate, which is very evident. Duplicate documents are issued in lieu of Original if it is lost or destroyed.
There is also a third category which is called a True Copy or Attested True copies, which are merely copies of the Original which are attested by an authorised person or a gazetted officer.
Hope this clears the matter to you, once and for all.
From India, Delhi