I realized that we had Hacker News for every day and wanted to compute the top PDFs for my own usage so I wanted to share with you guys.
My side project, Polar (https://getpolarized.io/) is used for managing PDF and other reading so you might want to check that out too. It's basically a tool for researcher, students, or anyone passionate about long term education and use read a great deal of technical and research material.
PDFs are supported but we also support offline caching of web page content. We also support Anki sync so you can create flashcards and sync them with Anki so that you never forget what you've read.
EDIT. Awesome! This landed on the home page in less than 15 minutes and is now #2.. Super excited you guys found this helpful. Great to contribute back to such an awesome community!