How to get text of particular text box by using Microsoft.Office.Interop.Word.StoryRange in C#4.0?

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C#

C#4.0

My C# Application interaction with Word Document using Microsoft.Office.Interop.Word. My Word Application having regular paragraph and also the range of the text in text box.So, I have easily accessed the particular paragraph and highlighted by the following way...

int start = wordDoc.Paragraphs[st_para].Range.Start;
int end = wordDoc.Paragraphs[ed_para].Range.End;
Microsoft.Office.Interop.Word.Range r = wordDoc.Range(start, end);
r.Select();

But now i want to do the same thing for the text that are not part of the main body of the Word Document.for that i am using Microsoft.Office.Interop.Word.StoryRange in the following way:

int start = wordDoc.StoryRanges....(Here i want to give the range like     paragraph)
         int end = wordDoc.StoryRanges......(Here i want to give the range like     paragraph)

         Microsoft.Office.Interop.Word.StoryRanges s = wordDoc.StoryRanges;
         Microsoft.Office.Interop.Word.Range r = s[WdStoryType.wdTextFrameStory];
         //r.SetRange(start, end);
         r.Select();

         while ((r = r.NextStoryRange) != null)
         {
             MessageBox.Show("text:"+r.Text);
             r.Select();
         }      

In the Above code iterate all the range of the text one bye one.But i want to get only particular text box value through start and end variable.
Please guide me to get of this issue...

Advance Thanks to All,
P.SARAVANAN.