How to add document protection element in existing xml document by using C# programmatically

Hi All,

I want to add text to existing xml element by using C#

The below am providing xml document please have a look.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<?mso-application progid="Word.Document"?>

<w:wordDocument xmlns:aml="http://schemas.microsoft.com/aml/2001/core" xmlns:wpc="http://schemas.microsoft.com/office/word/2010/wordprocessingCanvas" 
                xmlns:dt="uuid:C2F41010-65B3-11d1-A29F-00AA00C14882" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
                xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:v="urn:schemas-microsoft-com:vml" xmlns:w10="urn:schemas-microsoft-com:office:word" 
                xmlns:w="http://schemas.microsoft.com/office/word/2003/wordml" xmlns:wx="http://schemas.microsoft.com/office/word/2003/auxHint" 
                xmlns:wne="http://schemas.microsoft.com/office/word/2006/wordml" xmlns:wsp="http://schemas.microsoft.com/office/word/2003/wordml/sp2" 
                xmlns:sl="http://schemas.microsoft.com/schemaLibrary/2003/core" w:macrosPresent="no" w:embeddedObjPresent="no" w:ocxPresent="no" xml:space="preserve">
 <w:ignoreSubtree w:val="http://schemas.microsoft.com/office/word/2003/wordml/sp2"/>

<o:DocumentProperties><o:Title>Sample</o:Title><o:Author>xyz</o:Author><o:LastAuthor>pqr</o:LastAuthor>/o:DocumentProperties>

</w:wordDocument>

I want to add the below text how to do that by using C# programmatically

 <w:documentProtection w:edit="read-only" w:formatting="on" w:enforcement="on" w:unprotectPassword="C782CE28"/>

After adding my xml document should look like below;

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<?mso-application progid="Word.Document"?>
<w:wordDocument xmlns:aml="http://schemas.microsoft.com/aml/2001/core" xmlns:wpc="http://schemas.microsoft.com/office/word/2010/wordprocessingCanvas" 
                xmlns:dt="uuid:C2F41010-65B3-11d1-A29F-00AA00C14882" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
                xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:v="urn:schemas-microsoft-com:vml" xmlns:w10="urn:schemas-microsoft-com:office:word" 
                xmlns:w="http://schemas.microsoft.com/office/word/2003/wordml" xmlns:wx="http://schemas.microsoft.com/office/word/2003/auxHint" 
                xmlns:wne="http://schemas.microsoft.com/office/word/2006/wordml" xmlns:wsp="http://schemas.microsoft.com/office/word/2003/wordml/sp2" 
                xmlns:sl="http://schemas.microsoft.com/schemaLibrary/2003/core" w:macrosPresent="no" w:embeddedObjPresent="no" w:ocxPresent="no" xml:space="preserve">
  <w:documentProtection w:edit="read-only" w:formatting="on" w:enforcement="on" w:unprotectPassword="A983CE68"/>
  <w:ignoreSubtree w:val="http://schemas.microsoft.com/office/word/2003/wordml/sp2"/>
<o:DocumentProperties><o:Title>Sample</o:Title><o:Author>xyz</o:Author><o:LastAuthor>pqr</o:LastAuthor></o:DocumentProperties>
</w:wordDocument>

Can any one tell me how to achieve this by using C# programmatically?