I would like to give the client (person filling out the form) the option to download a PDF copy of their completed form. (the same kind of copy that I can get in my desktop app by right clicking the record and selecting 'Downlaod Response as PDF form'.
Can i add another button next to the submit button, or a link on the confirmation page for this to happen?
There is no way for him to get a copy currently. The best you could do is provide a submission receipt that includes the data in the email body. (Options tab -> Submission Receipts)