Add functionality to a Javascript based web app

I would like to add functionality to a web app and also do two minor edits. The website is called [login to view URL] I would like to make the following changes (see video screencast below): [login to view URL] Add functionality - Paid registration and login system. You can use any opensource system you'd like for the registration system, or something you've developed before. Standard registration asking for name, email, password -> send confirmation email. Monthly/yearly payment system using Stripe (or similar system). - Once user is logged in, it will take them to the app ([login to view URL]) where they can add and view their notes. The app uses Laverna opensource note taking app (see github for documentation: [login to view URL]). It is written in JavaScript. - Make it possible to upload and view a pdf next to the editing area. - Make it possible to add notes to a pdf file by selecting a text area in the pdf file and then add a corresponding note. This note can be clicked and goes to the section highlighted in the pdf. (Similar functionality to the Chrome extension called Hypothesis). Minor edits - Remove "Full screen" view and "Preview" view, instead have "Normal" view as the only default. - When editing a post, I should be able to press anywhere on the message area to start editing. See ckeditor's inline editor. That is what I need.