EDIT
I have jailbroken the iPad with Absinthe and installed AppSync Unified through Cydia. From there, I went to the mtmdev.org website and downloaded old .ipa files of IOS 4 and 5 apps, including iBooks! I've put these details down so if anyone else has the same issue, they can find the solution, because not one single solution worked for me, only this combination which was unclear and difficult to piece together, and involved multiple solutions and troubleshooting from many, many different sites!
Original post
I have been gifted an original iPad (IOS 5.1.1). It cannot be updated.
I don't need it for much, but I need to be able to read .pdf documents on it.
It has had a factory reset, so I cannot access previously downloaded apps on it.
I cannot download iBooks.
I have never previously downloaded apps on any device through the Apple store, so I cannot download 'previous purchases' at all.
What do you use to read your .pdf documents on such an old iPad?
I would only like to hear from those who have been successful, as internet searches have got me running around in circles, banging my head against brick walls. Thanks in advance :)
Adobe reader ?