Google Play Books does not always let you export books for offline reading. When it does, it uses DRM (Adobe Digital Editions), but some books lack this option—such as the digital edition of Land of the Lustrous that I purchased. There’s no way to figure this out ahead of time, so what I have are three books that I simply cannot read on the device of my choosing. So let this be a warning: do not ever buy books from Google, and really, do not ever buy anything from Google. It’s not yours and never will be.