All actions described above are available in the contextual menu, the XHTML submenu of the main menu and in the Author custom actions toolbar.
A drag and drop with a file from the Project view or from the DITA Maps Manager view to a DITA topic document that is edited in Author mode will create a link to the dragged file (the xref DITA element with the href attribute) at the drop location. A drag and drop with an image file from the default file system application (Windows Explorer on Windows, Finder on Mac OS X, etc) will insert an image element (the image DITA element with the href attribute) with the location of the dragged file at the drop location, like the Insert Graphic toolbar action.