WPA Actions are typically assigned to the toolbar buttons and combo boxes.
They can also used with the method ProcessWPA(),
i.e. WPDLLInt1.ProcessWPA "Size", "18.5"
In the PackageFile Manager you can click on 
to display a sorted table with the available names. It can also automatically create C# template code or XML lines to be inserted in the edit layout:
You only need to fill in the index of the image use the image list which is displayed on the right side of the editor to find the correct index.
Tip: Use 
to update the toolbar in the test application at once.