Highlighting a text in PDF using C#

Hi,
 
I am using below code to exract text from pdf file,

public string ReadPdfFile()
{
    string strText = string.Empty;
    try
    {
        PdfReader reader = new PdfReader(@"\\FilePath");
 
        for (int page = 1; page <= reader.NumberOfPages; page++)
        {
            ITextExtractionStrategy its = new iTextSharp.text.pdf.parser.SimpleTextExtractionStrategy();
            String s = PdfTextExtractor.GetTextFromPage(reader, page, its);
                    
            s = Encoding.UTF8.GetString(ASCIIEncoding.Convert(Encoding.Default, Encoding.UTF8, Encoding.Default.GetBytes(s)));
            strText = strText + s;
 
        }
        reader.Close();
    }
    catch (Exception ex)
    {
    }
    return strText;
}

This code returns all the text from one page of the PDF file, I need to highlight any word of my choice on that PDF page with yellow colour.
 
Any ideas how to do that?
 
Regards,
Kane