To open a database in 4D Developer using drag and drop, simply drag the database file onto the 4D Developer application.

The following files can be used:

Mac OS:
.4dbase
.4db
.4dc
.4dlink

Windows:
.4db
.4dc
.4dlink

Please see the 4D v11 SQL Design Reference for more information regarding opening options.
4th Dimension Documentation