A feature like drag-and-drop seems like something that needs to be provided at either the application level or within Tk or both.  While there is apparently no built-in Tk support for drag-and-drop, it appears to be possible to use a Tk extension that provides that capability and that will work with Tkinter.  See, for example, http://stackoverflow.com/questions/14267900/python-drag-and-drop-explorer-files-to-tkinter-entry-widget