You can drag documents in the following circumstances.
Drag to copy documents from the vault to any folder on your computer.
Drag a document from a local view into a vault view to check it in. The Check In Document dialog box appears.
Drag the local document onto a specific document in the vault to create a reference to that document.
Drag items from the Task Pane into the SolidWorks window to:
Add a component to an assembly
Add a library feature to a part
Open a SolidWorks document
Create a standard 3 view drawing by dragging a part or assembly into a drawing document (only if the part or assembly does not have annotation views)