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)

WorksheetPageSetup pageSetup = workbook.ActiveWorksheet.WorksheetPageSetup;
pageSetup.PrintTitles.RepeatedRows = null;
pageSetup.PrintTitles.RepeatedColumns = null;

        static void Main(string[] args)
        {
            string filePath = "Lorem ipsum dolor sit amet.pdf";
            //load a random document
            PdfFormatProvider provider = new PdfFormatProvider();
            RadFixedDocument originalDocument;
            using (Stream stream = File.OpenRead(filePath))
            {
                originalDocument = provider.Import(stream);
            }
            //draw something on the first page
            FixedContentEditor editor = new FixedContentEditor(originalDocument.Pages[0]);
            editor.GraphicProperties.IsFilled = true;
            editor.GraphicProperties.FillColor = RgbColors.Black;
            Telerik.Documents.Primitives.Rect Rect = new Telerik.Documents.Primitives.Rect(10, 10, 200, 100);
            editor.DrawRectangle(Rect);

            //export the pages as images and build a brand new document from the images
            SkiaImageFormatProvider imageProvider = new SkiaImageFormatProvider();
            imageProvider.ExportSettings.ImageFormat = SkiaImageFormat.Jpeg;
            imageProvider.ExportSettings.ScaleFactor = 0.8;
            imageProvider.ExportSettings.Quality = 80;


            RadFixedDocument doc = new RadFixedDocument();
            foreach (RadFixedPage page in originalDocument.Pages)
            {
                byte[] resultImage = imageProvider.Export(page);
                RadFixedPage pdfpage = doc.Pages.AddPage();
                editor = new FixedContentEditor(pdfpage);
                Stream imageStream = new MemoryStream(resultImage);
                editor.DrawImage(imageStream);
            }

            //export the pdf built from the images
            PdfFormatProvider pdfFormatProvider = new PdfFormatProvider();
            string outputPdf = @"output.pdf";
            File.Delete(outputPdf);
            using (Stream output = File.OpenWrite(outputPdf))
            {
                pdfFormatProvider.Export(doc, output);
            }
            Process.Start(new ProcessStartInfo() { FileName = outputPdf, UseShellExecute = true });
        }

        static void Main(string[] args)
        {
            string filePath = "Lorem ipsum dolor sit amet.pdf";
            //load a random document
            PdfFormatProvider provider = new PdfFormatProvider();
            RadFixedDocument originalDocument;
            using (Stream stream = File.OpenRead(filePath))
            {
                originalDocument = provider.Import(stream);
            }
            //draw something on the first page
            FixedContentEditor editor = new FixedContentEditor(originalDocument.Pages[0]);
            editor.GraphicProperties.IsFilled = true;
            editor.GraphicProperties.FillColor = RgbColors.Black;
            Telerik.Documents.Primitives.Rect Rect = new Telerik.Documents.Primitives.Rect(10, 10, 200, 100);
            editor.DrawRectangle(Rect);

            using (Stream output = File.OpenWrite(filePath))
            {
                provider.Export(originalDocument, output);
            }

            using (Stream stream = File.OpenRead(filePath))
            {
                originalDocument = provider.Import(stream);
            }
            //export the pages as images and build a brand new document from the images
            SkiaImageFormatProvider imageProvider = new SkiaImageFormatProvider();
            imageProvider.ExportSettings.ImageFormat = SkiaImageFormat.Jpeg;
            imageProvider.ExportSettings.ScaleFactor = 0.8;
            imageProvider.ExportSettings.Quality = 80;


            RadFixedDocument doc = new RadFixedDocument();
            foreach (RadFixedPage page in originalDocument.Pages)
            {
                byte[] resultImage = imageProvider.Export(page);
                RadFixedPage pdfpage = doc.Pages.AddPage();
                editor = new FixedContentEditor(pdfpage);
                Stream imageStream = new MemoryStream(resultImage);
                editor.DrawImage(imageStream);
            }

            //export the pdf built from the images
            PdfFormatProvider pdfFormatProvider = new PdfFormatProvider();
            string outputPdf = @"output.pdf";
            File.Delete(outputPdf);
            using (Stream output = File.OpenWrite(outputPdf))
            {
                pdfFormatProvider.Export(doc, output);
            }
            Process.Start(new ProcessStartInfo() { FileName = outputPdf, UseShellExecute = true });
        }