According to Nate Hoffelder at The Digital Reader (Confirmed: Harry Potter eBooks Are NOT DRM-Free in Kindle Format (Or Any Other eBookstore)):
I’ve heard back from Amazon, and guess what they told me?
“All titles that are pushed wirelessly from Pottermore to Kindle, or to other retailer’s eBook services and readers, are DRM encrypted at Pottermore’s request.”
That is not what Pottermore said at the press conference. You can check any account from any of the press who attended. All reported that the ebooks would be DRM-free.
Read more and continue to follow this story at The Digital Reader.