If you're a developer or just interested in the inner workings of Microsoft's products, the company does have quite an extensive library of eBooks to offer via its Virtual Academy. While the documents included are indeed free to download, they require an account.
If you don't want to mess around with that, there are posts like these in which you'll find download links for eBooks sans account. Yet another of these account-less freebies has popped up, and it's related to Azure.
Put together by Barry Luijbregts - Azure MVP - and Michael Crump - Technical Product Manager at Azure -, the second edition of "The Developer's Guide to Microsoft Azure" is an eBook written "by developers for developers". It provides a rundown of Azure capabilities, how the service handles different scenarios like scaling and logging, and even has a chapter dedicated to security.
If you're interested, you can grab it at this link.