That's why you should never buy DRM-ed anything if you intend to keep it long term. Companies change, businesses get bought & sold, collapse, disappear - thinking that your particular DRM scheme would be supported for 20 years is insane. For a movie that you'll forget in the next 2 days it's ok, for a book that you intend on re-reading years late - no reason to "buy" DRM-ed version of anything. Or, at least, if you have no other options, strip DRM from it immediately and export into a common format.