I recently knew a latex-editor "gummi", see http://gummi.midnightcoding.org/ , which is written by GTK+ graphical interface toolkit. There are two panels, one in the left which is an editor (using the library gtksourceview) and on in the right which is a viewer (using the library poppler). I am curious that if we can do similary things for every program. For example, replace the editor with "terminal"?"emacs"?"vim"?"terminator (a multi-windows terminal)"...etc. And replace the viewer with other viewers, which in my mind is Adobe Reader. With discussion with the author, he mentioned:

The viewer component is also replacable, but doing it with Adobe Reader would not be easy or perhaps even impossible. The reason for this being that Adobe Reader is a complete program instead of a library, and also closed-source

So I have some questions:

a) We can only make "library" embedded as a panel, but we can't do this for a (any) program?

b) Could we replace the editor with emacs? with terminal?

c) Could we replace the viewer with Adobe Reader? If not, why? Because it's a program or it's closed-source?

I know the questions in this thread are not very precise, sorry.