@GabiAPF: Nevermind, everyone with fewer than 10 posts is allowed to make mistakes
The dev forum is the right place to ask this - because the developers drop by here more regularly than in the parent forum, but I'm unsure which thread is better suited. Probably this one though, not the general kite thread. Oh, and yes, cross-posting is indeed frowned upon here - that's what knc1's comment was mostly about.
As to the specific problem: Sorry, can't help with neither kite nor kindlepdfviewer, nor the k3 actually. Just wait some time, and you'll probably get answers.
And BTW, knc1's suggestion in the other thread was a good one. Let it charge. On a wall charger, for an entire day, and ignore the light and screen. Then try to restart it.
I moved the posts from the other thread over to here. That's why the order of the first 6 posts might look a bit chaotic.