Most publishers use fairly weak DRM. Epubor relies upon the appropriate reader program (Adobe Digital Editions or Kindle). I was using an open-source plugin to Calibre, but Epubor seems easier and more reliable.
I bought a book from Taylor and Francis that used VitalSource; I hadn’t been aware of this format; it is horrible. I couldn’t find a workable DRM stripper, but fortunately T&F gave me a refund.
Most of my training classes lately has used VitalSource.
Apparently they take their DRM pretty seriously, and hide their keys pretty well, and rotate them often.
There's some older DRM strippers for it that no longer work, I'm guessing anybody that has a working set of key extraction won't tip their hat on it.
Of course lo-tech methods can work well enough.
And FWIW: Kindle seems to be switching over to ePub as the default method.
I bought a book from Taylor and Francis that used VitalSource; I hadn’t been aware of this format; it is horrible. I couldn’t find a workable DRM stripper, but fortunately T&F gave me a refund.