Boox Note Air or Nova 2. Nova 2 is more for books at 7.8" but can PDFs in a pinch. They are eInk but run Android and can run the Play Store. The built in PDF reader is good, ePub is ok. There is some jank using third party apps because they are expecting an LCD screen but a little tweaking generally gets them usable.

You might also want to take a look at Kobo's 10" model the Elipsa.