gtk-file-chooser-set-current-name (chooser name)
Sets the current name in the file selector, as if entered by the user. Note that the name passed in here is a UTF-8 string rather than a filename. This function is meant for such uses as a suggested name in a "Save As..." dialog. You can pass "Untitled.doc" or a similarly suitable suggestion for the name.
If you want to preselect a particular existing file, you should use the functions gtk-file-chooser-set-filename or gtk-file-chooser-set-uri instead. Please see the documentation for those functions for an example of using the function gtk-file-chooser-set-current-name as well.