Secure web pages

is there a way to create a secure web page a browser cannot view by typing the url.

i want to be able to have a browser pay for a product from my site via paypal…afterwhich, paypal will direct them to a secure webpage for download.

the only thing is, i dont want that person to be able to give the link to his or her buddies and rip off my product.

thanks in advance,
Andre