I have the latest Dropbox App installed on an iPad Pro 2018 running iOS 12.1.4, as well as on my 2012 MacBook Pro.
When trying to open Numbers/Keynote/Pages files in those iPad apps from my Dropbox, I get the message that "file cannot be saved." (There is no issue on the MacBook.)
If I duplicate the file on my MacBook and save it to iCloud, the file will download and open on the iPad, so the issue seems to be the ability to pull from my Dropbox.
I've deleted and re-installed the Dropbox App, switched App Refresh on/off, and done a ****** reset of the iPad. Any thoughts?