Largest collection of FREE Microsoft eBooks ever, including: Windows 8.1, Windows 8, Windows 7, Office 2013, Office 365, Office 2010, SharePoint 2013, Dynamics CRM, PowerShell, Exchange Server, Lync 2013, System Center, Azure, Cloud, SQL Server

The below blog of Eric Ligman "Microsoft Senior Sales Excellence Manager" contains more than 1 million free e-books, Step-By-Steps, Resource Guides, etc., .

It contains a lot of formats: PDF, DOC, epub, mobi.

Reference: Microsoft Free E-books