Do you, like me, simply HATE the fact that some ebook publishers and sellers like to lock you down with DRM (Digital Rights Management) software on their ebook files? DRM is used by publishers to restrict what you can do with your ebooks. DRM controls which devices you can use to read your ebook, and stops you converting your ebooks from one format to another. Rude.
I firmly believe that once you've purchased said ebook, then it should be yours to do with however you wish within the bounds of the law, of course. But that is another rather open-ended argument...
I buy ebooks from a few different sources, and if they come encumbered with DRM I use a plugin with Calibre that easily strips that rubbish away. I am then able to convert, copy and share the ebook file as I wish. The way it should be.
If this is something that you wish to look into, I can wholly recommend Apprentice Alf’s blog which is "intended to help anyone looking for free and simple software for removing DRM from their Kindle ebooks, stripping DRM from their Adobe Digital Editions ebooks, getting rid of DRM from their Barnes and Noble ebooks, freeing their Kobo ebooks of DRM, deleting the DRM from their Sony eBooks, or decrypting their Fictionwise eReader ebooks."