I want to create a menu where multiple files(mostly pdf) are shown and user can download them. I want to update those files, and add new when required without user having to download my app again. How can I do that?
you will need some webspace rented somewhere or have to set up some machine in your home as public server (not recommended due to security risks)
There you can upload files and make them available for example via HTTP (or HTTPS) or FTP.
If you search for ftp/http file download for c# there is a lot of tutorials on how to set this up client side.