Open from device option allows to select any diagram with the .drawio extension stored on your device, insert it into the page and, if necessary, update it using the editor. The uploaded diagram will be stored in the page’s attachments.
After the Open from device button click, the file manager will be shown.
Note: only files with .drawio extension are available for selection, no more than one file at a time.
After the diagram is selected and uploaded, a diagram editor opens setting the uploaded diagram as a source.
When you have finished working with the diagram, click the Save & Exit button to save the changes and exit editor or Exit to discard the changes made (if any) and leave.
After that, you'll see the preview of the uploaded diagram.