Uploading a Dropbox document to Lumin:
In Lumin, open the Documents menu.
Click the Upload button.
Select the Dropbox option.
Log in to Dropbox (if you haven't already).
Select the file (or files) you need and click Choose.
Selected files display in Lumin with the Dropbox icon displayed in the Storage column.
Syncing your changes:
In Lumin, open the Dropbox document you have imported.
Make your document edits.
Once done, click the Sync button in the top toolbar.
A sync success message is displayed.
NOTE: When the document is synced, any edits you make in Lumin PDF are synced back to the source document in Dropbox.