RIM has announced that the Playbook now supports EPUB DRM (Digital Rights Management. In the future there may be an e reader app and it will be able to read epub documents.
Adobe® Reader Mobile SDK is a software development kit (SDK) enabling mobile device and software developers to embed PDF and eBook support into their products. This ecosystem is used worldwide by thousands of publishers, libraries and content providers selling and lending millions of eBooks.
Read more at the Blackberry Dev Blog.
You can check out the Adobe Reader Mobile SDK here.