test.cs

// default value
float m_DPI = 96;

public Form1()
{
    InitializeComponent();
    // use the system DPI
    m_DPI = CreateGraphics().DpiX;
}

private void textControl1_TextMiniToolbarInitialized(object sender,
  TXTextControl.MiniToolbarInitializedEventArgs e)
{
    // add separators to all groups
    foreach (RibbonGroup group in e.MiniToolbar.RibbonGroups)
    {
        group.ShowSeperator = true;
    }

    // create a new group
    RibbonGroup rgPrint = new RibbonGroup()
    {
        ShowSeperator = false
    };

    // add new group to mini toolbar
    e.MiniToolbar.RibbonGroups.Add(rgPrint);

    // create new RibbonButton
    RibbonButton rbPrint = new RibbonButton()
    {
        // get the resources from the ResourceProvider
        SmallIcon = ResourceProvider.GetSmallIcon("TXITEM_Print", m_DPI),
        LargeIcon = ResourceProvider.GetLargeIcon("TXITEM_Print", m_DPI),
        Text = ResourceProvider.GetText("TXITEM_Print"),
        KeyTip = ResourceProvider.GetKeyTip("TXITEM_Print")
    };

    // set the tool tip
    rbPrint.ToolTip.Description = ResourceProvider.GetToolTipDescription("TXITEM_Print");
    rbPrint.ToolTip.Title = ResourceProvider.GetToolTipTitle("TXITEM_Print");

    // attached a click event
    rbPrint.Click += RbPrint_Click;

    // add a RibbonButton to the new group
    rgPrint.RibbonItems.Add(rbPrint);
}

private void RbPrint_Click(object sender, EventArgs e)
{
    textControl1.Print("MyDocument");
}