To enable Kanban Tool Dropbox integration, please go to "Settings". Next choose "Power-Ups" tab and click on "Dropbox". Now you can add files directly from your Dropbox account.
To add a file from Dropbox, click on the "+ add attachment" link, and choose "Attach from Dropbox" from the dropdown menu.
Dropbox power-up helps you keep documents and tasks together. You can add files from your Dropbox account to any task and collaborate on them.