It renders PDFs, let's you scale/move where on the screen the page is rendered, let's you flip through pages, let's you switch to a view of page thumbnails, let's you go to a page number, remembers the last page you were on.

If you expect more from your ebook reader than that, it is not just because of software.

As a sibling comment mentions that might be fixed soon. V1 had long since had support for third party apps. V2 is taking a bit of time (because controlling eink screens in weird) but will probably have third party apps support soon. At that point you will be able to use one of the well known open source ebook reading apps.

Edit: And to be clear, all the third party app support is unofficial, the help menu on the tablet includes the ssh password for root, everything past that is just reverse engineering (it's a pretty typical linux system apart from the display).