Using the Dropbox Power-Up
Enabling the Power-Up
To enable the Power-Up, open the board menu on the right side of the page, select the Power-Ups menu option, and then click the "enable" button next to the Dropbox Power-Up.
Authenticating with Dropbox
Once the Power-Up is enabled for the board, each individual user will need to authenticate their Dropbox account from within Trello. To do that, open up a card, click the Dropbox button in the Power-Ups section on the back of the board, and select "Attach a File" or "Attach a Folder."
A popup window will open. Click "sign in" and log in with your username and password. If you're already logged in, click "allow."
Using the Power-Up
You can access the Power-Up from the back of the card by clicking the Dropbox button in the Power-Up section. From there, select whether you want to attach a file or folder.
Once you make your pick, you'll be given the option to navigate through Dropbox's files or folders and select the file or folder you want to attach. Attached files will look like attached files uploaded directly to Trello, with the option to open those files in Dropbox.
Attached folders will also have an option to open them in Dropbox.
Removing Files and Folders
To remove a file or Folder, click the "remove" link underneath the file or folder's name on the back of the card.
Disabling the Power-Up
To disable the authorization with your Dropbox account, open the Power-Ups menu on the right side of the board. Then, click the gear icon and select "Remove Personal Settings". From there, select the option to clear data.
Disabling the Power-Up will not cause any data loss. It will change the formatting of the links in the card to be the same as any other attached links (just like how non-Business Class users would see the links on the card when the Power-Up is enabled).