[DllImport("User32.dll", EntryPoint = "FindWindow")]
        private static extern IntPtr FindWindow(string lpClassName, string lpWindowName);

        [DllImport("user32.dll", EntryPoint = "FindWindowEx")]
        static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpClass, string lpszWindow);

        [DllImport("user32.dll ", EntryPoint = "SendMessage")]
        public static extern IntPtr SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, string lParam);

        [DllImport("user32.dll", EntryPoint = "SendMessage")]
        public static extern IntPtr SendMessage(IntPtr hwnd, int wMsg, IntPtr wParam, IntPtr lParam);

        const int WM_CHAR = 0x0102;
        const int WM_SETTEXT = 0x000C;
        const int VK_RETURN = 0x0d;

        static void Main(string[] args)
        {
            IntPtr handle = FindWindow(null, "Hello.txt - 记事本");
            handle = FindWindowEx(handle, IntPtr.Zero, "Edit", null);
            if (handle == IntPtr.Zero)
            {
                Console.WriteLine("没有找到句柄");
                return;
            }
            SendMessage(handle, WM_SETTEXT, IntPtr.Zero, "Hello word!");
            SendMessage(handle, WM_CHAR, (IntPtr)VK_RETURN, IntPtr.Zero);//Enter
        }