Digital Rights Management (DRM) is the effort to control copying and sharing or downright piracy. It was once very common for PC game software, and it is currently the rage in music (think iTunes) and movies (think MPAA).
Cory Doctrow is an author who generally gives away his work while also selling it. He is not a fan of DRM. You might be interested to read this post by Cory Doctrow from the blog “Boing Boing” about the childrens’ book The Pig and the Box which is about sharing vs. DRM.
You might also like to examine the site from which the book may be purchased AND from which it may be downloaded in PDF format (free).
Be sure to click the “Home” link after you check out The Pig and The Box. There are more books with similar themes. I love the one about the crow.