I use the OneDrive app on macOS to sync files from a Sharepoint library. Most of the files are not actually downloaded yet - when you open them from Finder they download and then open. This applies to opening files from the File>Open dialog box in most applications as well (i.e. Illustrator).

However, Acrobat doesn't do this. If I choose a non-downloaded file it just closes the dialog box and never opens the file. I have to go through Finder and open it there instead.