The Dropbox app for iOS has an extremely misleading 'Open With' menu that only provides two options for PDFs: 'Adobe Acrobat Reader' and 'Add Text or Signature'. The expected behavior for most iOS users is that this would open the share sheet so that the PDF could be worked with in another app. Instead, that functionality is hidden behind the ellipses menu.
Additionally, most of the other top-level buttons in the UI revolve around the notion that the file is going to be shared with someone and commented upon, which I think is a poor assumption to make considering the core product offering has been file sync and backup. It's quite annoying to be forced into a different workflow and have things require way more steps than necessary to achieve the same goals as much earlier versions of the app. Making the iOS share sheet a top-level button would be a good start, but an even better option would be to allow the user to hide all the collaboration nonsense if that's not what they want from Dropbox.
