How can i write and read Microsoft Word .docx files using StreamWriter?

Hi. I am working on a project, and i need to be able to open a Microsoft word file outside of Unity. Unfortunantely i can't open the .docx If i Edit the file using StreamWriter, if i try, Microsoft Word Crashes with the following report:

I can however Read it through StreamWriter.

Anyone know how to prevent this?

Here is the Code i used:

 #pragma strict
 
 import System.IO;
 var input = "";
 var filePath = "test.txt";
 
  
 
 function Update() {
     if (Input.GetKeyDown("r")) {
         WriteFile(filePath);
     }
     if (Input.GetKeyDown("f")) {
         ReadFile(filePath);
     }
 }
  
 function WriteFile(filepathIncludingFileName : String)
 {
     var sw : StreamWriter = new StreamWriter(filepathIncludingFileName);
     sw.WriteLine("Name:");
     sw.Flush();
     sw.Close();
 }
 
 function ReadFile(filepathIncludingFileName : String) {
     var sr : StreamReader = new StreamReader(filepathIncludingFileName);
 
     input = "";
     while (true) {
         input = sr.ReadLine();
         if (input == null) { break; }
         Debug.Log("line="+input);
     }
     sr.Close();
 }

Thank you for taking your time reading this, i'm looking forward to your response :D