[Teknikal]

I just posted about the mess of the Android file system, my guess is you just need to find your actual real SD card on Moon+ Google purposefully confuses the issue by called the internal storage sdcard even though it isn't, On my phone I need to go back a folder or two until I see storage then go there and from there external_sd then I select my books folder. Unfortunately between different OEMS this location can vary but you should find it under either storage or 0 and sometimes both sometimes.

The irony is Google claimed before Micro SD cards are too confusing for users while that's actually the only part of my storage I can make any sense off at all, and on KitKat yes they did restrict things but you should still be able to import and read your books ,my G3 is on Kit Kat still and I can.

Really I think Googles behind the whole mess on purpose because they want people to pay them to use their cloud, they really see any type of local storage as a bad thing for their business which is just making Android harder and harder to use.