The eBooks in your HFS Digital Library may be downloadable in any of three file formats: PDF, ePub, or MOBI. You select this format when you purchase the eBook from the publisher's website. The eBook format you choose must be compatible with your computer, handheld device, or eReader.  Free software is available for nearly all computers and handheld devices that will read all three of these formats. If you intend to read your eBook on a dedicated eReader--such as an Amazon Kindle, Barnes and Noble Nook, Sony Reader, or Kobo eReader Touch--you should check that your device supports the eBook format you select.

PDF eBooks are readable on most computers and handheld devices using Adobe Reader. Some operating systems and browsers are also able to read PDF files without Adobe Reader using built-in tools. PDF eBooks are more similar to printed books than ePub and Mobi files are: the text of the book is "set" in a fixed layout on the page. This makes PDF a good format for larger screens, such as computers or tablets, but less ideal for smaller screens, such as smartphones or eReaders.

ePub files, unlike PDFs, are "reflowable" eBooks. This means that the text of the book is not in a fixed layout on the page; instead, the text can wrap and resize to be readable on many different screens. ePub files are compatible with most dedicated eReaders, with the notable exception of the Amazon Kindle.  

Mobi is the file format best suited for the Amazon Kindle. Amazon offers free Kindle apps for most platforms (PC, Mac, iPhone, iPad, Android, and others) that are capable of reading Mobi files.