using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace SendWmKeyup
{
    public partial class Form1 : Form
    {
        [DllImport("User32.dll")]
        static extern int SendMessage(IntPtr hWnd, uint wMsg, UIntPtr wParam, IntPtr lParam);

        [DllImport("user32.dll", SetLastError = true)]
        public static extern IntPtr FindWindowEx(IntPtr parentHandle, IntPtr childAfter, string className, IntPtr windowTitle);

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            System.Diagnostics.Process[] p = System.Diagnostics.Process.GetProcessesByName("notepad");
            IntPtr childHandle = FindWindowEx(p[0].MainWindowHandle, IntPtr.Zero,"Edit", IntPtr.Zero);

            SendMessage(childHandle, (uint)0x0100, (UIntPtr)0x00000041, (IntPtr)(0x001E0001));
            SendMessage(childHandle, (uint)0x0102, (UIntPtr)0x00000061, (IntPtr)(0x001E0001));

            SendMessage(childHandle, (uint)0x0100, (UIntPtr)0x00000041, (IntPtr)(0x401E0001));
            SendMessage(childHandle, (uint)0x0102, (UIntPtr)0x00000061, (IntPtr)(0x401E0001));

            SendMessage(childHandle, (uint)0x0101, (UIntPtr)0x00000041, (IntPtr)(0xC01E0001));
        }
    }
}