iCloud syncing My Documents and Desktop

I have a 2009 IMac and and an 2017 iPhone. I just got an 8th generation iPad, and ever since I started using it the documents (i.e., pdfs of word docs, spreadsheets, etc.) that were the Documents folder and on the desktop of my iMac kept showing up on my iPad and iPhone. I couldn't find a setting to stop just My Documents and my Desktop folders from syncing across all devices. If I turn off iCloud altogether, I lose emails, bookmarks, messages on the mobile devices. I finally just deleted the documents that were backed up to iCloud, and then moved them to a back-up drive instead of the hard drive on my computer.

Is there an easier way to keep documents from downloading to the iPad and iPhone?