iCloud, iCloud Drive, Docs

I have both Documents and PDF Expert and couldnt be more confused as to how file management is coordinated between them. At first glance it appears they are synced between both apps, yet only one of the apps has its own iCloud Drive folder (a physical folder as opposed to the open-from). Add to this additional devices and FAQ that vaguely mentions files should be copied between local and iCloud Drive, but that just sets up the user for more confusion since presumably only one of those files will be the most recent and unlike the sync capability between Documents and third party clouds, it doesnt appear there is the same capability for iCloud. To put this disaster in a sentence, I dont understand the logic between using local documents that get backed up to iCloud and that of iCloud Drive. It appears I have duplicates but not sure if I created them or not. Finally, the app retains links for items Ive opened or pushed to Documents from other apps. Are these copies of files, hard links to the primary file, or or something else?
Readdle, consistency is important an the file system on the apps should appear and function similarly. A graphical depiction of the file system between iCloud, iCloud Drive, and how it functions between apps would be very helpful!

LAX20531 about Documents: File Manager & Docs, v6.0.1