As per https
/www.dropboxforum.com/t5/Dropbox-files-folders/Dropbox-not-adding-a-place-to-MS-Project-2016-de..., Project, Visio, And I'm also assuming publisher are not supported by the Microsoft Office Add-In that Show's Dropbox as a save location in Microsoft Office Backstage.
Suggestion is that it supports all the Offices apps.