Basing on the increasing ebook commerce i had this idea. An integrated document viewer (evince, okular, just as examples) with which, in the same window, one can read the book and make moves on a board (to follow what the book is saying, i suppose :) )
I do not understand one thing: why integrating into Scidb? You can read the book with an external document viewer while Scidb is open.
of course but continuosly switching between the pdf window and the scidb window
Probably I still do not understand the idea of your request: If I integrate a document viewer into Scidb, the viewer will be opened with it's own window. What is the difference between this internal window and an external window (external document viewer)? In both cases (internal/external window) you have to arrange the window so that you can use both. In both cases the focus will switch to the window where you clicked last time with the mouse.
So a difference would appear only if I integrate the document viewer inside a sub-pane of the board window. This is possible only if I implement a flexible window layout (in planning stage). This means that this request should be postponed until the flexible window layout is implemented?!
Yes sure. I was not up-to-date about the stage of flexible window layout development, sorry