SP - having read your comment before it was removed, I went back and tried Calibre again. It states that Calibre will not remove DRM and there's a Calibre web page which explains why.
Perhaps you have an earlier version or something.
Also, I want to be able to use a book I paid for, for my own use. I'm not seeking to copy it for upload here, or anywhere else but, as Calibre explain, you don't buy these books - you sort of rent them - subject to a whole load of restrictions determined by Amazon, in my case.