Epub source code issue during extraction

Question

I'm trying to 'see' the source code for an interactive ebook (.epub) that I have on my ipad and it is running fine on Ibooks app.

What I did is changing the ebook's file extention .epub to .zip and unzipping it. The problem is that whenever i try to open the files inside the epub folder they are completely messed up:

where is the problem? (The book I tested with is on itunes store "the wind and the sun")

Answer 1

The book is encrypted using Apple's FairPlay DRM.