New manual is being prepared.
Some instructions by Booxstor, how things work in a new pdf reader are in this thread no more than 1 month back.
You may set as your default reader an old pdf reader, if you prefer it or want to wait for a manual.
I would say that the new pdf reader is let's say beta-version approaching release candidate state. Hopefuly we'll have stable pdf reader soon.
I like a new pdf reader and prefer it to old one
. But the fact, it is not fully finished and stable should be expressed.