iBooks Store: How do I know what format is used?
Books from the iBooks Store are always in the .ibooks or .epub format. It is never PDF.

Books from the iBooks Store can be DRM-protected, but they don't have to be. It is up to the publisher of the book to decide.

To check for DRM you can select the book and choose "Get Info" from the Files menu. If this shows "Purchased book" it is non-DRM, if it shows "Protected book" it is DRM-protected.