DRM is evil and restricts what you can do with legitimately baught content.
Ebooks
Use the DeDrm_tools Calibre plugin. It supports removing DRM from purchased Kindle content but requires use of an older Kindle version.
When decrypting print-replica Kindle ebooks, use KindleUnpack (also available as a Calibre plugin) to extract the pdf. Print replica ebooks are just a PDF with some Amazon-specific wrapper.