When attempting to import some DBF files on Mac OS, 4D may not recognize the format of the files and may not display those files in the import open-file dialog. This is due to a file type that does not match the type 4D is looking for. This problem can originate from, for example, the application with which the export was done or a network copy that altered the file type.
To correct that problem, you simply need to assign the file type "F+DB" to the file you want to import. You can perform that operation using either Resorcerer or ResEdit.