How to make the online viewing of documents on the site?

I have some objects in my page (such as libraries, schools, etc.). It is possible to add files to a specific object (.pdf, .doc, .xls, .png, .img). Files are stored in a file system on a server.

Now, I must implement a function for online document viewing directly on the site in the selection of the object, ie when the user clicks on an object, it opens at the bottom of the list of its documents, and when he clicks on a specific doc, it opens the online viewing.

Q: How can I make online viewing directly on the site?

There are services that are loaded in the doc and it gives you a link and you just embed code to your page, but the problem is that I have to dynamic loading docs and a lot of them.