Simple Android PDF viewer based on pdf.js and content providers. The app doesn't require any permissions. The PDF stream is fed into the sandboxed WebView without giving it access to the network files content providers or any other data.

Content-Security-Policy is used to enforce that the JavaScript and styling properties within the WebView are entirely static content from the APK assets along with blocking custom fonts since pdf.js handles rendering those itself.

It reuses the hardened Chromium rendering stack while only exposing a tiny subset of the attack surface compared to actual web content. The PDF rendering code itself is memory safe with dynamic code evaluation disabled and even if an attacker did gain code execution by exploiting the underlying web rendering engine they're within the Chromium renderer sandbox with less access than it would have within the browser.