I have designed a website for an author who wants to sell his book as a physical book and also as a download. The book has over 200 images and a lot of custom formatting and is proving to be a nightmare to convert to an ebook. I've seen many authors selling their books as PDF downloads. What is the best way to protect the PDF file? The book is 396 pages long. The PDF is about 85 MB, is that too large to offer as a download? Are there ways to make the file smaller (other than zip)?