C#

[Flags]
public enum SWP
{
      SWP_ASYNCWINDOWPOS = 0x4000,
      SWP_DEFERERASE = 0x2000,
      SWP_DRAWFRAME = 0x20,
      SWP_FRAMECHANGED = 0x20,
      SWP_HIDEWINDOW = 0x80,
      SWP_NOACTIVATE = 0x10,
      SWP_NOCOPYBITS = 0x100,
      SWP_NOMOVE = 2,
      SWP_NOOWNERZORDER = 0x200,
      SWP_NOREDRAW = 8,
      SWP_NOREPOSITION = 0x200,
      SWP_NOSENDCHANGING = 0x400,
      SWP_NOSIZE = 1,
      SWP_NOZORDER = 4,
      SWP_REDRAWONLY = 0x717,
      SWP_SHOWWINDOW = 0x40
}

[DllImport("User32.dll", CharSet=CharSet.Auto)]
public static extern bool SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter, int X, int Y, int cx, int cy, int uFlags);

private static SWP hideFlags = SWP_NOSIZE | SWP_NOMOVE | SWP_NOZORDER | SWP_NOREDRAW | SWP_HIDEWINDOW

// Put this in your code instead of ShowWindowAsync
SetWindowPos(p.MainWindowHandle, IntPtr.Zero, 0, 0, 0, 0, hideFlags);

Encoding enc = Encoding.GetEncoding(1251); // Cyrillic
using (TextReader reader = new StreamReader(path, enc, true))
{
  // Strings are stored in Unicode in the CLR so encoding
  // isn't a problem here since the characters have already
  // been decoded.
  string content = reader.ReadToEnd();
 
  // Proceed with your regular expressions.
}