how to open .txt file with out using system.diagnostics.process

I don't think it makes sense to avoid Process, but:
[System.Runtime.InteropServices.DllImport("shell32.dll")]
private static extern long ShellExecute(Int32 hWnd, string lpOperation,
string lpFile, string lpParameters, string lpDirectory, long nShowCmd);

private enum SW
{
SW_HIDE = 0,
SW_SHOWNORMAL = 1
}
private void OpenNotepad()
{
ShellExecute(0, "open", "notepad.exe", null, null, (long)SW.SW_SHOWNORMAL);
}