Tried to buy this from the front page: there's a Buy It Now button, but on my Android 'phone clicking it doesn't do anything. In fact, I can't find an active link to let me buy this at all. I'll try later on a Windows PC and see if that works.
EDIT: By holding the Buy It Now button and selecting the option to open in a new tab I was able to buy the PDF on my 'phone, but trying to simply click the button does nothing except highlight the text. I suspect this may be specific to the Chrome browser running on Android.