Drag-and-drop index file

Is there a way to add an index-file to a database using drag-and-drop? I’ve tried ⌃-drag, ⌥-drag, ⌘-drag, as well as adding ⇧. Nothing seems to work.

Command-option-drag, discussed in the Importing and Indexing section of the manual. Works to index folders and their contents as well.

Thanks.