Of course, they put your name & other info on every page of the PDF generated for you. That probably works as a general "shaming" mechanism, such that most folks won't share indiscriminately.
O'Reilly doesn't seem to do that, unless it's embedded in the PDF in a way which doesn't show up in simple viewers. Pragmatic Bookshelf, Manning and Packt (out of the e-books I have handy for quick checking) do put your name/address on the bottom of every page to discourage piracy. Edit: Specifics for each publisher, for anyone who's curious: Manning - Name and email address on each page Pragmatic Bookshelf - Name on…
The other (regular, relased) books from ORA don't.