Here is an example. The dll must be added to the OpenSpan installation folder and imported to the Toolbox as a .Net Component.  In your Visual Studio Solution, you can simply add a Component Item to your solution and it will extend the ComponentModel Class. 

/*
 * Author : Mitchell Vega
 * Date : 07/31/2017
 * Description : This class shows a model of how a custom component can be created to use alongside OpenSpan. The constructors should be left alone. All public methods are accessible from the Toolbox once they have been imported. In this example, I have written a method called StartNotepad.
 * Notes : Project DLL must be in the OpenSpan installation folder. This DLL will be imported from the .Net Components Tab when importing to the Toolbox. Adding a reference in the OpenSpan project is NOT necessary for this to work.
 */

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Diagnostics;
using System.ComponentModel;

namespace ExampleLibrary {
    public partial class CustomComponent : Component {

        public CustomComponent() {
            InitializeComponent();
        }

        public CustomComponent(IContainer container) {
            container.Add(this);
            InitializeComponent();
        }

        public void StartNotepad() {
            Process.Start(@"notepad.exe");
        }
    }
}