The Barnes & Noble ebook (styled “nook”) is developed by American book retailer Barnes & Noble , B&N ebook have Barnes & Noble’s eReader DRM, sometimes called Secure eReader format. all other device doesn’t support B&N ebook drm, so user can’t read these books on Kindle, iPad, Sony e-reader unless remove DRM protection first.
this is tutorial how to remove B&N DRM, detail at