[Ken Maltby]

Not sure what "exit koreader via mnt/onboard" means, but when you poke the "Home" icon in the top menu of File Manager, you should see the full page Koreader PNG. You return to the Kobo software (Nickel) but the page is not automatically refreshed. You had to poke the screen to get the Header and Footer showing. In the header there is a "Home" icon, poke that to return to the Kobo Home page. If you just want to power off or sleep you can do it from when the full page Koreader PNG is displayed.

Non OCR'd PDFs are just images, for all practical purposes, and have never worked well on a small screen. I can read them on my AuraHD, but even there the text is smaller than I would normally like. There are work arounds but a larger screen is the best answer.

Luck;
Ken