Doc (an abbreviation for ‘document’) is a file extension for a document created by Microsoft Word, the most popular word processing program. The .doc format is used for MS Word versions of between 97 and 2003. The later version of 2007 uses a different format.
MS Word was first created in 1983 for Xenix systems under the name Multi-Tool Word. Later newer versions were written for several other platforms like DOS running IBM PCs in 1983, the Apple Macintosh in 1984, and SCO Unix, OS/2, and Microsoft Windows in 1989. The M Word programs have the ability to create and share documents using a set of writing tools. These documents may include formatted text, images, tables, graphs, charts, page formatting, and print settings.
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.