How to fill a bookmark in Wordml

[sweetpotatop]

Hello,

I have a locked Word document (save as XML) in which I need to fill out
the bookmark through ASP.NET
And part of the xml is shown below:

<aml:annotation aml:id="0" w:type="Word.Bookmark.Start"
w:name="ContactName" />
<w:r>
<w:rPr>
<w:b />
<w:sz w:val="24" />
</w:rPr>
<w:instrText> FORMTEXT </w:instrText>
</w:r>
....
....
<w:r>
<w:rPr>
<w:b />
<w:noProof />
<w:sz w:val="24" />
</w:rPr>
<w:t></w:t>
</w:r>

Can you show me how I can fill out that ContactName bookmark? Since I
am a newbie, I don't know how I can search the bookmark and then look
for the next available " <w:t></w:t>" tag.

Thanks in advance. Your help would be greatly appreicated.