I am not sure if .pdf's are available for this author, but I have always liked Linda Goodman. 'Star signs', 'love signs', 'sun signs', and 'relationship signs' are very good. They are crammed with a lot of information though, especially star signs which has horoscope information, numerology, lexigrams, energy working and color, and if I recall a smattering of crystal work as well.
I read star signs early on in my own learning and not very much of it clicked until I re-read the book a few years later. The other books are a little more focused though so they are easier to digest.
I really enjoyed The Only Astrology Book You'll Ever Need by Joanna Martine Woolfolk. It is a really big book but even in the first twnety pages she gives you some tables to reference on masculine or femenine, cardnial or mutable, which of the four elements, ruling planets, etc. I could not find a pdf for you but I would suggest looking at your local library. I was able to find this book along with others on astrology and tarot. You can also buy this book off Amazon for like fifteen bucks. I have added an Amazon link below to at least show you what the book looks like and so that you can see the reviews and opinions on it.
I took a hunt through my library of stuff and found another book that I -knew- i had but couldn't remember the name of.
'Do it yourself Astrology' by Lyn Birkbeck.
The book is sectioned in such a way you can go through each chapter with your (or someone elses) natal information and build a pretty solid astrological chart, and then has sections on how to interpret the different relations and influences of that chart. it isn't exactly something you read from cover to cover but more a tool where you learn through doing. It is fairly straightforward to do as well as long as you don't mind going over a few tables and charts.
Astrology for Dummies is actually a really good book to start with...I rented it from my local library in PDF format. Not exactly "free" but it is. Try taking a look with your library and see if they have it.
After getting through the first few chapters though,I realized I'd rather have it in hard-copy format just because I was constantly flipping through pages for reference. So unless you're going to take extensive notes, might be more worth it just to rent a paperback. :)