Apple has a history of abandoning users whenever they introduce a new product to the market. This wasn't always the case. The Apple IIgs, despite its 16-bit architecture, allowed for most of the old 8-bit Apple ][ software to run on the new system. However, since the introduction of OSX, the attitude has been, "Deal with it old-timers. We know what's best for you."
I am the proud owner of a first generation iPad 1. I use it to play music and read eBooks. It performs these two tasks as well as any modern iPad or iPhone does. Alas, in their attempt streamline the software, Apple removed to ability to transfer PDFs and eBooks to an iPad 1 from iTunes. The entire Books section has been removed from the product with the expectation that iPad users will now get their content from the cloud. The problem is that iCloud, Dropbox and other cloud storage systems no longer work on an iPad 1.
My attempts to Google a solution have had mixed results. Apple is no help. The user help forums are filled with bad advice. In my frustration I have figured out a relatively simple way to get files, especially books, to your iPad 1. In a nutshell, we are going to create a web page containing links to all your books and then, assuming your computer and ipad are on the same local wi-fi network, browse to that web site on our iPad to download the files to iBooks.