Teachers must enable Dropbox in the Assignment in order for Students to upload attachments for the assignment.

The download feature in the Assignment can be used to attach pdf documents for the Student to view for course work, but they cannot download the pdf in onCampus Attach. They must log into the full site through their browser.

Please review this Knowledgebase article for a demonstration of how Students use onCampus Attach: Can a student use an iPad Attach app to attach files to assignments?