I bought a second hand Kindle DX to read PDF's. I installed Duokan on it, which a 3rd party OS that has much better PDF handling and allows dual booting with Kindle OS. It also supports epub format.

It is very easy to use Kindle without an Amazon account as there are all sorts of tools to allow you to do pretty much anything you want on your Kindle.

AFAIK you can install Duokan on every Kindle version.