Untitled

string text = Clipboard.GetData(DataFormats.Html).ToString();

Version:1.0
StartHTML:0000000105
EndHTML:0000038765
StartFragment:0000038357
EndFragment:0000038725

<html xmlns:o="urn:schemas-microsoft-com:office:office"
xmlns:w="urn:schemas-microsoft-com:office:word"
xmlns:m="http://schemas.microsoft.com/office/2004/12/omml"
xmlns="http://www.w3.org/TR/REC-html40">

<head>
<meta http-equiv=Content-Type content="text/html; charset=utf-8">

**{... lots of HTML code with classes etc. etc. etc.. }**

<!--StartFragment--><span style='font-size:11.0pt;line-height:107%;
font-family:"Calibri",sans-serif;mso-ascii-theme-font:minor-latin;mso-fareast-font-family:
Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin;
mso-bidi-font-family:Arial;mso-bidi-theme-font:minor-bidi;mso-ansi-language:
EN-US;mso-fareast-language:EN-US;mso-bidi-language:HE'>Hello sir</span><!--EndFragment-->
</body>

</html>

text = text.Replace("Hello sir", "Bye sir");