About the different formats
PDF for Digital Editions / Ebook Reader
This means that the ebook was originally a PDF and has been encrypted to protect the author from the risk of piracy.
PDF is the most popular document publishing format for general use. You're probably familiar with PDF – it's the file format that normally opens up in Adobe Reader or Adobe Acrobat. In order to give users a simpler and "cleaner", less cluttered reading interface, Adobe developed Adobe Digital Editions (ADE), especially for reading ebooks. Most recognized book publishers release ebooks in "copy-protected", encrypted form and 'PDF for Digital Editions' is a popular choice.
The great thing about viewing PDF ebooks is that they retain the original design of each page – so you see on your screen exactly what the book designer intended. Formats that are more suited to smaller screens (like EPUB) tend to lose page formatting when displayed on a computer screen.
Which ebook format is for me?
For a Computer, Choose PDF
If you only expect to read your ebook on a computer (not on a phone or special ebook device), then you should choose a PDF-based ebook. This is because PDFs display the pages of a book exactly as they were designed by the book publisher. In other words, a PDF will usually maintain the design integrity of the original printed book. With other formats, pages can look different – sometimes radically different – when displayed.
For a Hand-Held Device, Choose EPUB
PDFs sometimes display awkwardly on small screens, while some the EPUB format is designed especially for reading on smaller screens. If you have a smart phone, PDA or special ebook reader device, then you should choose EPUB.
Although we suggest different formats for different devices, it is worth noting that some books are only available in only one format. Even if it is not the recommended format for your device, this does not mean that you will not be able to read the book perfectly well! Also the Online Reader is always another option.