To open an existing UI design class, right-click the file name in the Project Explorer view and select Open With. Then, from the sub-menu, select OpenEdge ABL Editor to display the source code, or OpenEdge Visual Designer to display the design.

You can also simply double-click the file name in the Project Explorer view. Progress Developer Studio for OpenEdge opens the form either in a Visual Designer editing window or in the ABL Editor, whichever you last selected when opening the file with the Open With command. If you have not previously used Open With for the file, it opens in the Visual Designer.
Note: You cannot open multiple instances of the same file in the Visual Designer. However, multiple instances of the file in the OpenEdge ABL Editor (via the New Editor command) are allowed.