You can create a flat file from the Toolbox, Browser, or Model menu.
Use the Flat File tool in the Toolbox.
Select Model > Flat Files to access the List of Flat Files, and click the Add a Row tool.
Right-click the model (or a package) in the Browser, and select New > Flat File.
For general information about creating objects, see Core Features Guide > Modeling with PowerDesigner > Objects.