I want to be able to import some pdfs that are in iBooks on my iPad to my Mac. I would preferably like to sync them via my iCloud account. On my 2016 MacBook Pro (Sierra 10.12.4), I have enabled the iBooks.app in iCloud in System Preferences. On my 2014 iPad Air 2 (iOS 10.2.1), I have selected Sync Books in Settings > Books. But I still cannot see these pdfs in my Mac's iBooks.
MacBook Pro with Retina display, macOS Sierra (10.12.2), 2016
The Settings > iBooks > Sync Collections and Sync Bookmarks And Notes settings don't copy items between devices - all that the Sync Collections setting does is if you have a book or PDF on both devices and you move it into a collection on one of them, it will be moved into the same collection on the other. Similarly the Sync Bookmarks And Notes setting requires the book to already be on both.
You might be able to copy them to your Mac's iTunes library via File > Devices > Transfer Purchases (that has always copied PDFs and/or epubs from the iBooks app, not just actual ibooks) and then do File > Move Books From iTunes in your Mac's iBooks app.
Or you might be able to use iCloud Drive to copy them (I don't use it, not sure what the benefits/cons of using it are) : Use iCloud Drive or iBooks to access your PDF files, ePub files, and books - Apple Support
Syncing pdfs from iBooks on my iPad to my MacBook Pro
