PdfFormatProvider provider = new PdfFormatProvider();
            RadFixedDocument document = provider.Import(File.ReadAllBytes("Landscape.pdf"));

                TextSearch searchText = new TextSearch(document);
                TextSearchOptions searchOptions = new TextSearchOptions { UseRegularExpression=false, CaseSensitive=false, WholeWordsOnly = true };
                IEnumerable<SearchResult> matchResults = searchText.FindAll("sed", searchOptions);
                foreach (SearchResult resultItem in matchResults)
                {
                    Rect rect = resultItem.GetWordBoundingRect();

                   
                    RadFixedPage page = resultItem.GetResultPage();
                    FixedContentEditor editor = new FixedContentEditor(page);
                 
                    editor.GraphicProperties.FillColor = new RgbColor(125, 255, 0, 0);
                    editor.DrawRectangle(rect);
                }
            
            string outputFilePath = "result.pdf";
            File.Delete(outputFilePath);
            File.WriteAllBytes(outputFilePath, provider.Export(document));
            Process.Start(new ProcessStartInfo() { FileName = outputFilePath, UseShellExecute = true });