Some authors and/or publishers of ebooks prefer using DRM, some do not. If you have an ebook on your Kindle or other device and would like to remove the DRM there are tools available to do this.
The link to the blog with information on DRM removal includes this note:
I hope that everyone uses these dedrm tools only for personal access to the ebooks they have bought. Large scale distribution of dedrmed ebooks is not a good idea. No help will be given to anyone doing so.
Blog on removing DRM from some ebooks. ( Link opens in new window)
NOTE: None of my ebooks have DRM. ( Link opens in new window)