Free SEO & Google AdWords Books
Below are 13 links to some great SEO and Google AdWords Whitepaper PDFs including information about SEO Audits, Conversions, Local 3 Packs, and a must-read guide to SEO Ranking Factors by SEMRush. If you have never used SEMRush before you need to check out their site. They have the best SEO and PPC tools on the web.
If you enjoy these PDFs I highly encourage you to visit the corresponding websites for more PDFs and website blog posts. Enjoy and learn!!