Multi-file support is enabled per file definition, and can then be applied to table definitions within the FD that utilize multiple files.
You can also right-click a table instance entry in the Table Definitions node and select Enable Multi-file.
The Enable Multi-File on FD dialog box is displayed.
In the FD, a new item, Label:<label-name>, is available.
Multi-file support is now enabled for any tables derived from this file definition. When you create a table definition, use the new item to create an additional column for the file label.