This is very clever, and only the tip of the iceberg on eBook security. To block printing of your .PDF eBook, if you want, you can easily embed watermarks and hidden fields that only show up when the .PDF file is printed. The bottom line is that a .PDF file can be protected and as much as any book, you can secure your copyrighted material. If a thief intends to steal, there is little anyone can do, and there's little use in worrying about it. All you can do is make it difficult for them, but they will find a way if they work at it long enough.
Nothing is completely secure in the technology world today.
The format is new and not nearly as dynamic as Acrobat .PDF, but with each passing day the applications and options are increasing. Adding pictures and internal links in this format are limited, and most of it is done when creating the original Word.doc file. Meaning, the file will be able to travel and be viewed in other applications and windows. The Microsoft Reader application appears as a book-like window on your screen, with arrows on either side of the page number up top right of the each page. So, again you are limited to the way Microsoft has decided to allow you to navigate through the pages.