This is fermatslibrary.com a platform to annotate scientific papers. But I don't understand why that paper you cited is there - it's easy to read already.

FTA: "This is the first chapter of Michael Nielsen's book Neural Networks and Deep Learning."

The book itself is CC BY-NC 3.0.

I'm guessing that the creator simply printed the webpage (without link on the header/footer), and has honestly referenced the source on the first comment. So probably there was no malice intended.

I did however leave a Disqus comment on how they could make it clearer. The ones I could think of -- either print HTML to PDF with a link on the header, or modify the source of the page to add a note before you printing to PDF.