Duokan License?
 

Is Duokan an open source project? Is there a license somewhere? I'd like to modify it and release my modifications to the public.

Hahahahahhaahahahahahahahahhhaahhaahahahah.

Sorry, couldn't resist.

In short: No, they're probably in violation of every OSS license under the sun.

I use Duokan for long time on my K4 (no internet) specially for the ability to read PDFs and EPUBs much better than the Kindle itself. Do you think that it's dangerous to use it only because it's Chinese ?

Not because it is "only" Chinese, because it is in violation intellectual property rights.

The Chinese National government has made multiple statements on intellectual property rights.
Eventually they will get around to the violators, stand them against a wall, and shoot them.
But it is a big country and it will take time for that to happen.

I don't think it's that dangerous to use as long as you don't connect to wifi, just my personal opinion.

You are right. I use it as a real book. Books are downloaded from my PC