Sorry, I don't have any idea what's that workflow demo 8)

You could use the "Flowcharter" sample project that comes with the trial version as a starting point:
https://www.mindfusion.eu/FCNetDemo.zip

It lets you add new objects by drag-and-drop from a toolbox, and has a property grid that lets you change some attributes of the selected items. There's also a second toolbox that lets you change the shape of link arrowheads.

If you need to let the user draw boxes on the canvas instead of using drag-and-drop, set the DiagramView.Behavior property to LinkShapes.

I hope that helps,
Stoyan

That sample lets you add new objects too, but only through drag-and-drop over a link. The idea of that sample is to show how you can let users build a workflow in a more controlled manner, so it does not let you draw new nodes at random locations nor connect nodes arbitrarily.

You can certainly enable drawing new nodes and links; just comment out the view.Behavior = Behavior.Modify; line in the NewWorkflow() method. You could also modify the drag/drop event handlers to allow creating nodes via drag-and-drop at any location and not only over existing links.

I hope that helps,
Stoyan