Also, Apple sucks at services when they fail. I'm not sure it's the only way, but it's the only way I found that worked. TL DR thread summary: you can force a re-sync by "deleting" the iBooks app from the iPad and reinstalling it. Has anybody encountered and FIXED this somehow? I've signed in and out of iCloud, enabled/disabled auto-downloads for iBooks, restarted the iPad, and toggled virtually anything toggleable - on both iPads. Not "there but with the cloud logo" or "there but halted", just - not there. The odd thing is: ALL PDF Files are shown in iCloud storage (in iPad Settings -> General -> Storage & iCloud Usage -> Manage (iCloud) Storage -> iBooks), but they are NOT shown in the iBooks app itself, and will not download.
When I attach the iPad to a Mac and transfer purchases, that's the third that gets transferred to the Mac - it simply doesn't see the rest. Only about a third of them transferred to the new iPad through iCloud backup restore. When downloading PDF or other files from iBook store, the downloading process cant be accomplished. Within 90 days of purchase, you will be able to do this. Type Apple Books in the search bar and press Enter button. Once installed, open it and go to App Store.
I'm moving from an iPad Air 2 to a new 10.5" Pro (very, very slick), and I've got a rather large collection of music PDFs in iBooks on the old machine, sorted into various lists - practise books, music theory, exercises, fake books, etc. If you still can’t download the iBook, you can ask for a refund. Once you got iPadian, here are the steps to follow to install iBooks for PC Windows: First of all, download iPadian software on Windows. To get rid of it, tap on the update, then Delete. Here you will find the pending update in the list of apps. I'm in a bit of a bind due to the black box that is iCloud. To find the iOS update download, tap on Settings, General then Device name Storage.