If it’s Adobe it can be made DRM-free relatively easy. It’s the first thing I do with every purchase (and legal where I live). Try Calibre (free/libre) or Epubor (paid but more versatile and works better for me).

Amazon has just introduced a policy change that probably makes it much harder (or impossible) to de-DRM stuff bought there, so I’m going to do without the books exclusive to them for the time being.