gistfile1.cs

// introduce extension method:    
    
    public static class VieweExtensions
    {
        public static bool IsSidebarVisible(this Sidebar sidebar)
        {
            return
                sidebar.ParametersPanel.Visible | sidebar.SearchPanel.Visible |
                  sidebar.ThumbnailsPanel.Visible | sidebar.TocPanel.Visible;
        }
    }
// Sample of usage : viewer1.Sidebar.IsSidebarVisible();