Microsoft Doc Format:
In computing, DOC or doc (an abbreviation of 'document') is a file extension for word processing documents; most commonly for Microsoft Word. Historically, the extension was used for documentation in plain-text format, particularly of programs or computer hardware, on a wide range of operating systems. During the 1980s, WordPerfect used DOC as the extension of their proprietary format. Later, in the 1990s, Microsoft chose to use the DOC extension for their proprietary Microsoft Word word processing formats. The original uses for the extension have largely disappeared from the PC world.
Binary DOC files often contain more text formatting information (as well as scripts and undo information) than files using other document file formats like Rich Text Format and HyperText Markup Language, but are usually less widely compatible.
The DOC format varies among Microsoft Office Word Formats. Word versions up to 97 used a different format from Microsoft Word version between 97 and 2003.
ePub is now a standard e-book file format that is supported by almost* every e-book reading device include Sony Reader, BeBook, IREX Reader, iPad, iPhone and the upcoming Nook from Barnes & Noble's.
Other than hardware devices, you can also read .epub books on your desktop or mobile phone using free e-reader software like Stanza, Mobipocket, FBReader (for Linux), Aldiko (for Android) or Adobe Digital Editions.
Amazon Kindle uses a proprietary format (AZW) and cannot read ePub files directly though you can use the free Stanza desktop application to convert an ePub ebook into AZW (or even PDF), a format that your Kindle can understand.