I then clicked on the cloud icon in the bottom left corner to begin syncing with iCloud. After this had been completed, I tried syncing with my iPhone and found the reference details were synced but there were no PDFs, although the attachment icons were present. I looked in the iCloud Drive folder on my Mac and did indeed see a "Bookends" folder. Inside, there was a single file: "Bookends Cloud Test.txt." I had also been monitoring my network activity and was sure the PDFs were not being uploaded during sync.
I then came across the user guide page (http://www.sonnysoftware.com/bookendsontap/docs/ ). When going into the Preferences and looking at the attachment location, I tried selecting "iCloud Folder For iOS Sync." I noticed one or two references began to say they couldn't find the attachment (this may be a coincidence) and I thought I should stop to avoid causing any issues.
To set up iCloud syncing, what should be my next steps for Bookends under both macOS and iOS after importing my Sente library (under macOS)? When syncing, will the macOS and iOS versions of Bookends each keep local versions of the attachments too, or only access the documents from iCloud?
Thanks in advance for your help!