Sample C# code for executing any type of mouse click on a WebBrowser control by calling a set of unmanaged functions from the user32.dll library.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
 
namespace BrowserMouseClick
{
    public partial class Form1 : Form
    {
        [DllImport("user32.dll", CharSet = CharSet.Auto, SetLastError = false)]
        static extern IntPtr SendMessage(IntPtr hWnd, uint Msg, IntPtr wParam, IntPtr lParam);
 
        [DllImport("user32.dll", SetLastError = true)]
        static extern IntPtr GetWindow(IntPtr hWnd, uint uCmd);
 
        [DllImport("user32.dll", CharSet = CharSet.Auto)]
        static extern int GetClassName(IntPtr hWnd, StringBuilder lpClassName, int nMaxCount);
 
        public Form1()
        {
            InitializeComponent();
        }
 
        private void Form1_Load(object sender, EventArgs e)
        {
            webBrowser1.Navigate("http://www.devpub.com");
        }
 
        private void btnMouseClick_Click(object sender, EventArgs e)
        {
            int x = 100; // X coordinate of the click
            int y = 80; // Y coordinate of the click
            IntPtr handle = webBrowser1.Handle;
            StringBuilder className = new StringBuilder(100);
            while (className.ToString() != "Internet Explorer_Server") // The class control for the browser
            {
                handle = GetWindow(handle, 5); // Get a handle to the child window
                GetClassName(handle, className, className.Capacity);
            }
 
            IntPtr lParam = (IntPtr)((y << 16) | x); // The coordinates
            IntPtr wParam = IntPtr.Zero; // Additional parameters for the click (e.g. Ctrl)
            const uint downCode = 0x201; // Left click down code
            const uint upCode = 0x202; // Left click up code
            SendMessage(handle, downCode, wParam, lParam); // Mouse button down
            SendMessage(handle, upCode, wParam, lParam); // Mouse button up
        }
    }
}