Learning Latin is my dream, and I decided to try again, now that I've found this book.
I volunteer at Distributed Proofreaders (although, I had nothing to do with this particular project).
That would be wonderful if they could have both the PDF and HTML versions.
That is actually possible, and some people do produce PDF versions in addition to other formats. I don't think there are many of them, though, and to me it seems complicated... It involves working on TEI (Text Encoding Initiative -- special XML-based markup), and when you are done, apparently, you can generate plain text, HTML and PDF from this one file in TEI. In principle, it sounds great! In practice, some people have said that currently the HTML versions generated from TEI weren't up to our standards.
PDFs can also have hyperlinks to sections... I've seen a math textbook in PDF with links, produced by one volunteer. But I have no experience in this area. I just do HTML and plain text.