The Project Gutenberg has the greatest collection of books on the web. Their ebooks were previously published by bona fide publishers and digitized by them with the help of thousands of volunteers. I just downloaded "From the Earth to the Moon" by Jules Verne onto my ereader and this is how you do it.
From the Earth to the Moon" it's here. On that page click on Download. Like most pages of this type the trick is to ignore all the other stuff on the page, and yep, there's a lot of it. Clicking Download takes you to the next page where you will have to make a selection based on the type of ereader you have. Don't worry, it's not all that difficult. If are reading on an iPad, an iPhone, an Android, a Sony Reader, a Kobo, a Nook or just about anything else, choose EPUB. If you have a Kindle, choose Kindle. Kindle doesn't support the EPUB format, because, well, they don't have to. Except for Kindle, EPUB is the industry standard format for ebooks.
How to manage your ebooks using Adobe Digital Editions.