References and PDF's can be added to either your
The two libraries will synchronize whenever Mendeley Desktop is opened. The libraries can be synchronized at any time by clicking on the Sync button on the Mendeley Desktop toolbar.
You can control which folders in your Mendeley libraries are synchronized by going to the All Documents folder in your Mendeley Desktop library and clicking on the Edit Settings button.
Note! The Edit Settings screen will also display your Web Space usage. If you are running out of space you may choose to deselect Synchronize attached files.