EtherPK ( https://app. etherpk. com ) now reads, annotates, signs and manages PDFs: Click a link to a PDF in your notes and it opens in a tab inside the app, where you can read it, mark it up, fill in forms, sign and save a copy.
Source: [Hacker News](https://blog.etherpk.com/pdf-reading-annotation-and-signing-inside-your-markdown-notes)