The key to a solution is analysis of the problem statement. The comments about a clipboard imply a solution. The actual requirement appears to be that the customer wants to open a Notepad window with text in it, where the text is from a text box.
Process notepad = new Process();
notepad.StartInfo.FileName = @"notepad.exe";
notepad.EnableRaisingEvents = true;
Note. This solution was found on the web. It was modified for clarity, i.e. the process object is "notepad" and WaitForInputIdle was reduce to 1 second.
If someone has the time to look into an improvement to this code, then one question is, can the completion of WaitForInputIdle be trapped as an event which invokes the SendKeys.SendWait method?