How to save pdf files, images and view them with React?

Hi all,

This is my first post, sorry if I do wrong.
I am really new to this, I am apprehending a lot thanks to this great community and I have come to this problem, I was recommended to save my files in a directory on the server, but I think the reactivity is lost.

I ask for your help in the steps that I must follow and how to do it,

Greetings from Bolivia.