View files in the browser but do not download them

What technology do I use to create a website where an administrator uploads files (pdf, powerpoint, word, excel) and users (according to permissions) view it in the browser but can only see it? They can't copy or download it.

It would be like an FTP server but that the files (pdf, pwpt, word and excel) are NOT downloadable but can be viewed in the browser.

It would use CSS so that they cannot select text to copy it, and would disable the "download" button by hiding it.