Download PDF to iPad using iBooks 

Alternative options here: www.discoverte...
Because iPads and iPhones don't have their own dedicated file management system for offline files, it isn't always obvious how to save electronic publications so that you can access them when you're no longer connected to the internet.
The official "Apple" advice is to use their iBooks App to manage this process, so this is the video walk-through of that process. The post in the link above also walks through another method (using Adobe Reader).