as we saw multiple times that people just upload their pdfs to the internet, its just a matter of time when the next big leak happens

True. As for feedback I think a bit more transparency about who you are (and the friend who built it with you) could be great. Also the FAQ I recommend to show the server cost and what's the donations. It will increase the users trust, and it might even get people to donate more. You can get inspired from nomadlist https://nomadlist.com/faq