You would find and download it from the iTunes store.
On your iPad, use the App Store. This is basic and important: you cannot download ANY iPad app from any other web site or anywhere else except Apple's official stores.
Test Screen Name wrote:
On your iPad, use the App Store.
Yeah. Sorry. App Store. Not sure where I got iTunes from...
<Runs off to grab more coffee>
You can search for "Adobe Acrobat Reader" in the App Store app or tap the following link on your iPad:
Please let us know if you have additional questions.