Here are the 4 ebook formats that I think are most important to know about and understand
Epub stands for electronic publication. This is the most popular and most widely used of all ebook formats. Epub was designed by the Open eBook Forum and developed by the International Digital Publishing Forum.
Devices that can open this file include the iPhone, iPod Touch, iPad, Sony Readers, Kobo Reader, and the Nook from Barnes & Noble.
Mobi is short for “Mobi Pocket”. This format can be opened on a number of mobile devices and smart phones. Most notably it is used by the Amazon Kindle line of devices. There are also browser and computer based programs that can read Mobi format, including Kindle for Mac or Kindle for PC
This is an Amazon format used exclusively on the Amazon Kindle line of devices. It is basically a MOBI format that uses a high compression option. Amazon will accept books in AZW or Mobi format. If you use Amazon to convert your file from Epub or Microsoft Word it will be converted into AZW.
The Portable Document Format was created by Adobe for its Acrobat products. This is NOT a flowing text format like the other formats mentioned. PDF is a page based document format originally created for printed content. However, it is still a popular format used by many individuals and companies. PDF formats can be read in most browsers, computers, tablets, smart phones etc… However, on small devices like smart phones a PDF can be difficult to read.