To customize the tableOfContent in Active Report viewer, firstly we have to get all control from viewer and then get the Tab Control and work on TabPage.
var controls = viewer1.Controls.Cast(); foreach (Control control in controls)
{
// Check fot TableOfContents Control
if (control.Name == "TableOfContents")
{
// Getting the TabControl.
var contColletion = control.Controls;
Control tabCollection = contColletion[0];
TabControl tabControl = (TabControl)tabCollection;
tabControl.Appearance = TabAppearance.Normal;
// Remove the Thumbnail Tab from Control.
tabControl.TabPages.RemoveAt(1);
}
}