Nice work! To counterbalance the comments here a little bit, I think an email address for a book is more than a fair exchange. My one suggestion would be to hav

Nice work! To counterbalance the comments here a little bit, I think an email address for a book is more than a fair exchange. My one suggestion would be to have a HTML version, so that mobile users can read it easier. I do most of my reading on my phone and PDFs are really hard to read, since the text size doesn’t scale. This doesn’t need to be extra effort, you could probably just compile whatever underlying markdown document you probably have that you used to create the PDF and save it as a HTML file, and send link to it (or send the HTML file itself) after email signup alongside the PDF.