Make sure you have logged into your Dropbox account and authorised diagrams.net (draw.io) to store and edit diagrams stored there.

1. Go to app.diagrams.net and click Open Existing Diagram. If you are already in the diagram editor and using Dropbox to store your diagrams, select File > Open from the menu.
2. Navigate to the diagram file in your Dropbox folders, select it, then click Choose to open it in the diagrams.net editor.
   

Note: If you have stored a diagram file outside of the app>drawio folder, diagrams.net will copy it on an automatic save. This is because Dropbox only allows diagrams.net to store data in this specific folder.

You don’t need to manually save your diagram after you make changes to it - diagrams.net will save a new version of your diagram regularly while you are editing.

Work with your diagram’s revision history in Dropbox