I rebooted one more time, recalibrated the ink side, and opened the novel I've been reading. That works fine, so I opened a PDF I'd been reading yesterday with no trouble, and it works fine. I downloaded the digital edition of the magazine directly from the website (rather than through caliber) and that also works fine. So I've concluded that there was something problematic with the pdf I grabbed through caliber. What a relief! I would have been very sad to have to be without my PE for any length of time. Thanks for the suggestion!