Well the s3 works only in this way :
It limits the time to load that resource on user's machine .
It loads the resource from s3 for the given duration after it stops loading the resource .So anybody who wants to download the pdf from the same link in the dom will not be able to do so after a certain duration .
You can enable "disable right click" on course status page .
The pdf can be downloaded for certain amount of time .
As far as we know it cant be protected from downloading :
https://stackoverflow.com/questions/4930914/prevent-pdf-file-from-downloading-and-printing