Every part of the WinForms viewer — toolbar, side panels, scrollbars — can be shown or hidden at run time through the StiViewerControl properties.

Toggle viewer elements. Each option maps to a property; assigning it updates the preview immediately:
private void cbToolbar_CheckedChanged(object sender, EventArgs e)
{
    PreviewControl.ShowToolbar = cbToolbar.Checked;
}

private void cbBookmarks_CheckedChanged(object sender, EventArgs e)
{
    PreviewControl.ShowBookmarksPanel = cbBookmarks.Checked;
}

private void cbThumbs_CheckedChanged(object sender, EventArgs e)
{
    PreviewControl.ShowThumbsPanel = cbThumbs.Checked;
}

How it works. The viewer control exposes a property for every part of its chrome, letting you trim it down to just what your application needs.
На скриншоте ниже Вы можете увидеть результат выполнения данного кода:

Customizing the Viewer