There is no downloading to the iPad as you would expect from using a desk top computer or laptop. The only download-like action that is available is the "Open In..." function - where you can choose to open a file in a compatible app. In addition, there is no central location for downloading to. One, because the iPad doesn't do downloads and t*o, because of the sand boxing function of the iOS.
There is no central file system for apps (programs) to access so that you can open files. Each app has its own area - and it's not accessible to other apps.
The only way to access the file directory or system files is to jail break the iPad. Then, you can install various tweaks (iFile is the best one) that will allow you to access the full file system.
Sorry, but on a stock iPad, Apple has it pretty restricted, mainly for iOS security.
Marilyn