Select File > Project Properties in the main window.
Select Sources in the Project Properties window and click Add Source Root.
Use the Add Source Folder window to navigate to and choose the folder
containing your existing source code.
Verify the existing source code path is displayed in the Source Roots list
and click OK to add it to the project.
The IDE creates the project folder containing existing code, source packages, and libraries.
You can view, create and edit the project source code in the Source
Editor to finish creating your applet.