Chessbase vs Chessbase Viewer

I am considering purchasing an opening encyclopedia from the chessbase and it is a little bit hazy if what I am purchasing will be sufficient to use as is or will I need to buy any kind of other software? 

 It says that it has Chessbase Viewer 13 in it, but is this sufficient? I assume that chessbase viewer and chessbase are not the same thing, because the chessbase itself without any databases is for sale there for the same price as the opening enciclopedia. 

So can anybody explain what the difference is between chessbase viewer that goes with the opening encyclopedia and the chessbase? Will I need anything else after purchasing opening encyclopedia? 

Sorry for my ignorance, but I am quite new to the chessbase software and haven't used any of it before. I know the right place to ask would be chessbase support service, but I emailed them and haven't got an answer for 10 hours already.

I think that the GUIs are dif but I m not sure...

Chessbase Reader is a free program that provides a very basic interface with limited filtering.  It might meet your needs, depending on what you want to do.  It is apparently deemed adequate for the "opening encyclopedia" you're looking at.

"Chessbase" (the program) is an expensive, full-on database program, with lots of features not found in Chessbase Reader.