Started seeing this issue come up with the Beastiary when I purchased it last month. I don't believe I'm missing too many pages from that book, if it turns out that I am, I'll alert Paizo and we'll have to discuss how that will be dealt with. In the mean time, the Advanced Players Guide has some serious issues where I can't simply ignore a page here or there for some obvious reasons; and it would appear that the reason for the problem has to do with Paizo adding a security layer onto their books. While I can appreciate the need and desire to protect one's copyrights, this does not supersede one's legal obligations either. You have my contact information, please do so, so that we can discuss this problem in detail.