at System.Linq.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
   at System.Linq.Enumerable.Cast[TResult](IEnumerable source)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.MarkedContents.StructElementObject.CopyPropertiesTo(PostScriptReader reader, StructureElementsImportContext context, StructureElement element)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.MarkedContents.StructElementObject.CopyPropertiesTo(PostScriptReader reader, StructureElementsImportContext context, StructureElement element)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.MarkedContents.StructElementObject.CopyPropertiesTo(PostScriptReader reader, StructureElementsImportContext context, StructureElement element)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.MarkedContents.StructTreeChildrenObject.CopyPropertiesTo(PostScriptReader reader, StructureElementsImportContext context, StructureElementsCollection childElements)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.MarkedContents.StructTreeRootObject.CopyPropertiesTo(PostScriptReader reader, StructureElementsImportContext context)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.DocumentStructure.DocumentCatalog.CopyStructureTreeTo(PostScriptReader reader, IRadFixedDocumentImportContext context)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Elements.DocumentStructure.DocumentCatalog.CopyPropertiesTo(PostScriptReader reader, IRadFixedDocumentImportContext context)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Import.RadFixedDocumentImportContext.BeginImportOverride()
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Import.BaseImportContext.BeginImport(Stream pdfFileStream)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Import.PdfImporter.Import(Stream input, IPdfImportContext context)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.PdfFormatProvider.<>c__DisplayClass19_0.<ImportOverride>b__0()
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.ExceptionHandling.ExecutionHandler.TryHandleExecution[E](Action operation)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.PdfFormatProvider.ImportOverride(Stream input, CancellationToken cancellationToken)
   at Telerik.Windows.Documents.Common.FormatProviders.FormatProviderBase`1.Import(Stream input, Nullable`1 timeout)

14 0 obj
<< /A 16 0 R /Border [ 10 10 10 60 ] /Rect [ 411 36 565 48 ] /Subtype /Link /Type /Annot >>
endobj

   at Telerik.Windows.Documents.Utilities.Guard.ThrowExceptionIfTrue(Boolean condition, String message)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Types.IndirectObject.get_Content()
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Export.PdfExportContext.BeginExportIndirectObject(IndirectObject indirectObject, Int64 offset)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Model.Types.IndirectObject.Write(PdfWriter writer, IPdfExportContext context)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Export.PdfExporter.WritePendingIndirectObjects(IPdfExportContext context, PdfWriter writer)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Export.PdfExporter.WriteFontsFromContext(PdfWriter writer, IPdfExportContext context)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Export.PdfExporter.Export(IRadFixedDocumentExportContext context, Stream output)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.PdfFormatProvider.<>c__DisplayClass21_0.<ExportOverride>b__0()
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.ExceptionHandling.ExecutionHandler.TryHandleExecution[E](Action operation)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.PdfFormatProvider.ExportOverride(RadFixedDocument document, Stream output, CancellationToken cancellationToken)
   at Telerik.Windows.Documents.Common.FormatProviders.FormatProviderBase`1.Export(T document, Stream output, Nullable`1 timeout)

 //Step 1: Create an instance of XlsxFormatProvider to import the Excel file
            XlsxFormatProvider xlsxFormatProvider = new XlsxFormatProvider();
            Telerik.Windows.Documents.Spreadsheet.FormatProviders.Pdf.PdfFormatProvider pdfFormatProvider = new Telerik.Windows.Documents.Spreadsheet.FormatProviders.Pdf.PdfFormatProvider();

            Workbook workbook;
            using (FileStream input = new FileStream("Input.xlsx", FileMode.Open))
            {
                workbook = xlsxFormatProvider.Import(input, TimeSpan.FromSeconds(10));
            }

            //Step 2: Export the workbook to PDF RadFixedDocument to modify fonts
            Telerik.Windows.Documents.Spreadsheet.FormatProviders.Pdf.PdfFormatProvider spread_pdf_provider = new Telerik.Windows.Documents.Spreadsheet.FormatProviders.Pdf.PdfFormatProvider();
            RadFixedDocument fixedDocument = spread_pdf_provider.ExportToFixedDocument(workbook, TimeSpan.FromSeconds(10));

            foreach (var page in fixedDocument.Pages)
            {
                foreach (var content in page.Content)
                {
                    if (content is TextFragment text)
                    {
                        // Replace the font with Helvetica or HelveticaBold based on the original font style
                        text.Font = text.Font.Name.ToLower().Contains("bold")
                            ? FontsRepository.HelveticaBold
                            : FontsRepository.Helvetica;
                    }
                }
            }

            //Step 3: Save the modified RadFixedDocument back to PDF
            string outputFileName = "ExportedWorkbook.pdf";
            Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.PdfFormatProvider fixed_pdf_provider = new Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.PdfFormatProvider();
            using (FileStream output = new FileStream(outputFileName, FileMode.Create))
            {
                fixed_pdf_provider.ExportSettings.DocumentUnhandledException += ExportSettings_DocumentUnhandledException;
                fixed_pdf_provider.ExportSettings.FontEmbeddingType = Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Export.FontEmbeddingType.Subset;
                fixed_pdf_provider.Export(fixedDocument, output, TimeSpan.FromSeconds(10));
            }
            Process.Start(new ProcessStartInfo() { FileName = outputFileName, UseShellExecute = true });