Dropbox is fantastic. Transferring files from one device to another device can be challenging, but with Dropbox it's a dream.
Dropbox is essentially an online folder where you can store things and retrieve them from almost any device; your iPad, iPhone, iMac (Mac or MacBook) or PC or Android device.
Easy peasy. Simply open Dropbox, tap Upload, choose your files and let it do it's thing. It will send the file to your Dropbox account where you can download it from wherever you need it.
It took me a few minutes to work out how to DOWNLOAD a file from Dropbox to my other iPad, but it's easy now that I know how. Simply tap on the STAR in the top right hand corner which adds the file to your Favourites. This means the file will download to your device automatically, available for offline use. You can also open or save the files into any App that supports the file type you're downloading. For instance with one tap you can save any image in your Dropbox folder directly into your Camera Roll.
It's one of my Essential Apps for iPad that I'd recommend everyone has.