How to Replace the NEW Text inplace of old text if I have the coordinates?

Hi,

I am repalcing the Old text with new one "NEWText". But the new PDF does not contain anything but blank in place of old text. But Link annotation is working.

Q:2, Its replacing the first text found, not all the words in all pages? How to replace all words in all pages if the search text found?

TextSearch.ResultCode code = txt_search.Run(ref page_num, ref result_str, ref ambient_string, hlts);

                    if (code == TextSearch.ResultCode.e_found)
                    {
                        //add a link annotation based on the location of the found instance
                        hlts.Begin(doc);
                        while (hlts.HasNext())
                        {
                            pdftron.PDF.Page cur_page = doc.GetPage(hlts.GetCurrentPageNumber());
                            double[] quads = hlts.GetCurrentQuads();
                            int quad_count = quads.Length / 8;
                            for (int i = 0; i < quad_count; ++i)
                            {
                                //assume each quad is an axis-aligned rectangle
                                int offset = 8 * i;
                                double x1 = Math.Min(Math.Min(Math.Min(quads[offset + 0], quads[offset + 2]), quads[offset + 4]), quads[offset + 6]);
                                double x2 = Math.Max(Math.Max(Math.Max(quads[offset + 0], quads[offset + 2]), quads[offset + 4]), quads[offset + 6]);
                                double y1 = Math.Min(Math.Min(Math.Min(quads[offset + 1], quads[offset + 3]), quads[offset + 5]), quads[offset + 7]);
                                double y2 = Math.Max(Math.Max(Math.Max(quads[offset + 1], quads[offset + 3]), quads[offset + 5]), quads[offset + 7]);

                                Rect rectContaningText = new Rect(x1, y1, x2, y2);
                                ContentReplacer replacer = new ContentReplacer();
                                string replacement_text = "NEWText";
                                replacer.AddText(rectContaningText, replacement_text);
                                replacer.Process(cur_page);

                                pdftron.PDF.Annots.Link hyper_link = pdftron.PDF.Annots.Link.Create(doc, new Rect(x1, y1, x2, y2), pdftron.PDF.Action.CreateURI(doc, "http://www.pdftron.com"));
                                hyper_link.RefreshAppearance();
                                cur_page.AnnotPushBack(hyper_link);
                                
                            }
                            hlts.Next();
                        }
                        doc.Save(output_path + output_filename, SDFDoc.SaveOptions.e_linearized);