how to prevent pdf files save locally or forward the to anyone

OK, just for the hell of it, I did try it. For starters, I would never upload any file that I consider to be sensitive enough that I want to block access to it to an unknown server, especially not one that was registered in China (according to a WhoIs.net domain lookup I ran). You never know in whose hands (private or governmental) it will end up... And there's no contact information of any kind or any details about the owners, developers, etc. of this website. If a service is free I expect to at least know who is behind it. If not, I'm worried about their intentions, especially when they ask users to send them sensitive information.

Secondly, it took me less than 5 minutes to be able to download the original file I uploaded based on the "secure share link". Of course, the downloaded copy has no restrictions applied to it whatsoever. Anyone with a modicum of tech-savviness would be able to do the same.

In conclusion, your "protection" is worthless and your reason for offering this service is dubious, at best. Please stop spamming the forums with links to it.

What are you trying to achieve?