使用c#将word文档转换为文本文档

So I am currently trying to convert a word doc (.doc) into a text document because I want to use regular expressions on it to find things in the document. So I came up with the below and it converts the word document into a rich text format (by appending it to a rich text box), but this does not translate into a plain text format. When I tried with regular text document it printed every word on a new line. I have not been able to find any information on how to do this in C#. I'm using C# and visual studio 2010.So I am currently trying to convert a word doc