To create a new file and add it to a project

In Solution Explorer, right-click the project, and click Add > New Item.
Expand PL/I Items, and click Native (or, Native > Mainframe Subsystem).
Select a file type from the list, and click Add.
This creates a new file in the project, and opens the file in the editor.

By default, new PL/I source files have a .pli extension but Enterprise Developer also recognizes files with a .pl1 extension as PL/I source. By default, PL/I include files have an .inc extension but Enterprise Developer also recognizes files with an .in extension as include files.