外部アプリケーションにキーストロークを送り操作する - reves-phantasm @ ウィキ

宣言部

[DllImport("User32.dll", EntryPoint = "FindWindow")]
private static extern IntPtr FindWindow(String lpClassName, String lpWindowName);
[DllImport("user32.dll", CharSet = CharSet.Unicode)]
private static extern bool PostMessage(int hWnd, Int32 Msg, int wParam, int lParam);

private const Int32 WM_KEYDOWN = 0x0100;

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処理部

IntPtr hWnd = FindWindow(null, "Yahoo! JAPAN - Windows Internet Explorer");

if (hWnd == IntPtr.Zero)
{

 Console.WriteLine("ハンドルが取得できません");
 return;

}

bool result = PostMessage((int)hWnd, WM_KEYDOWN, (int)(Keys.F11),0);