Workbook wb = new Workbook();
            Worksheet worksheet = wb.Worksheets.Add(); 
            PatternFill fill = new PatternFill(PatternType.DiagonalStripe, Colors.Red, Colors.Transparent);
            worksheet.Cells[0, 0].SetFill(fill);

            string outputFilePath = "Sample.pdf";
            File.Delete(outputFilePath);
            Telerik.Windows.Documents.Spreadsheet.FormatProviders.Pdf.PdfFormatProvider pdfFormatProvider =
                new Telerik.Windows.Documents.Spreadsheet.FormatProviders.Pdf.PdfFormatProvider(); 
          
            //export to file
            using (Stream output = File.OpenWrite(outputFilePath))
            {
                pdfFormatProvider.Export(wb, output, TimeSpan.FromSeconds(10));
            }

            Process.Start(new ProcessStartInfo() { FileName = outputFilePath, UseShellExecute = true });