If the files are just AES-encrypted and the links are there, as the linked article suggest, it seems that it would be easy to create a standalone script to download and decrypt these.
Essentially, the key for decrypting the files is made up of the book owner's passphrase and the super-secret key embedded in the closed-source binary.
I wasn't able to reverse engineer the binary or extract that key.
If the files are just AES-encrypted and the links are there, as the linked article suggest, it seems that it would be easy to create a standalone script to download and decrypt these.