mozilla/pdf.js — reverse-engineered prompt

Build me a browser based PDF reader in JavaScript using HTML5, similar to Mozilla PDF.js.

I want to be able to open a PDF in the browser and read it without needing any plugin or desktop app. It should render the document pages clearly, let me move through pages, zoom in and out, and generally feel like a normal web PDF viewer. Please include a simple demo page so I can run it locally and test with sample PDFs.

Set it up so a developer can install dependencies, start a local server, and open the viewer in the browser. If there’s a production build step, include that too. Keep it focused on modern browsers first, but don’t make choices that would block older browser support later. Look up current PDF.js docs online if you need to.