KEEP AVAILABLE THE VIEWING OF A POST JUST FOR WHO IS REDIRECTED BY PAYPAL

Hallo there!
i was wondering if there was a way to hide the randomly visualization of a page, of a url, and keep it visualizable just for who come from paypal website, just for who is redirected from paypal;
i dont want to use login in my website;
i have created some buttons by paypal and put on the post;
i would like that just who push the button and go through paypal paying the fees for visualize and download the guide can visualize the destination page and not all randomly visitors can do it.
is there any solution for solve this situation?
thanks a billion who offer me the solution.
good bye