static void Main(string[] args)
        {
            FixedExtensibilityManager.ImagePropertiesResolver = new ImagePropertiesResolver();

            //Telerik.Windows.Documents.Extensibility.JpegImageConverterBase defaultJpegImageConverter = new Telerik.Documents.ImageUtils.JpegImageConverter();
            //Telerik.Windows.Documents.Extensibility.FixedExtensibilityManager.JpegImageConverter = defaultJpegImageConverter;

            //Output("fyb-64.png", "output-working.pdf");
             Output("fyb.png", "output-broken.pdf");
        }
        private static void Output(string resourceName, string outputFileName)
        {
            var document = new RadFixedDocument();
            using (var editor = new RadFixedDocumentEditor(document))
            {
                Stream image = new FileStream(resourceName, FileMode.Open);

                var table = new Table
                {
                    LayoutType = TableLayoutType.FixedWidth,
                    Margin = new Thickness(10, 0, 0, 0),
                };

                var row = table.Rows.AddTableRow();
                var cell = row.Cells.AddTableCell();
                var block = cell.Blocks.AddBlock();
                block.InsertImage(image);
                editor.InsertTable(table);

                var pdfData = ExportToPdf(document);
                File.Delete(outputFileName);
                File.WriteAllBytes(outputFileName, pdfData);

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

        private static byte[] ExportToPdf(RadFixedDocument document)
        {
            byte[] pdfData;

            using (var ms = new MemoryStream())
            {
                var pdfFormatProvider = new PdfFormatProvider();
                pdfFormatProvider.Export(document, ms);
                pdfData = ms.ToArray();
            }

            return pdfData;
        }

            Telerik.Windows.Documents.Extensibility.JpegImageConverterBase defaultJpegImageConverter = new Telerik.Documents.ImageUtils.JpegImageConverter();
            Telerik.Windows.Documents.Extensibility.FixedExtensibilityManager.JpegImageConverter = defaultJpegImageConverter;

            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 });

System.OutOfMemoryException: Insufficient memory to continue the execution of the program.
   at System.Text.StringBuilder.ExpandByABlock(Int32 minBlockCharCount)
   at System.Text.StringBuilder.AppendWithExpansion(Char value)
   at System.Text.StringBuilder.Append(Char value)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Utilities.CrossReferenceCollectionReader.GetAllText(Reader reader, Int64 minOffset, Int64 maxOffset)
   at Telerik.Windows.Documents.Fixed.FormatProviders.Pdf.Utilities.CrossReferenceCollectionReader.FindAllObjectOffsets(Reader reader, Dictionary`2 tokenToOffsets, Int64 minOffset, Int64 maxOffset)

PdfFormatProvider pdfFormatProvider = new PdfFormatProvider();
byte[] exportedDocument = pdfFormatProvider.Export(document);
document = pdfFormatProvider.Import(exportedDocument);

16 0 obj
<</AP<</N<</Off null/On 188 0 R>>/D<</Off 189 0 R/On 190 0 R>>>>/AS/Off/F 4/FT/Btn/H/T/P 19 0 R/Rect[ 40.3 690.45 56.15 706.7999]/Subtype/Widget/T(Einraeumung:Grabnutzungsrechts)/Type/Annot>>
endobj

void WriteToPdf(RadFlowDocument document, Stream outputStream) {

   PdfFormatProvider pdfWriter = new() {};

   pdfWriter.Export(document, outputStream);
}

Parallel.ForEachAsync(listOfDocuments, (document, _) => {
   WriteToPdf(document, Stream.Null);
});

System.InvalidOperationException: Operations that change non-concurrent collections must have exclusive access. A concurrent update was performed on this collection and corrupted its state. The collection's state is no longer correct.
   at System.Collections.Generic.Dictionary`2.FindValue(TKey key)
   at Telerik.Windows.Documents.Fixed.Model.Fonts.FontsRepository.TryCreateFont(FontFamily fontFamily, FontStyle fontStyle, FontWeight fontWeight, FontBase& font)
   at Telerik.Windows.Documents.Flow.FormatProviders.Pdf.Utils.Extensions.CopyPropertiesFrom(CharacterProperties fixedProperties, PdfExportContext context, CharacterProperties properties)
   at Telerik.Windows.Documents.Flow.FormatProviders.Pdf.Export.PdfExporter.CreateListLevel(ListLevel flowLevel)
   at Telerik.Windows.Documents.Flow.FormatProviders.Pdf.Export.PdfExporter.CreateList(List flowList)
   at Telerik.Windows.Documents.Flow.FormatProviders.Pdf.Export.PdfExporter.ExportDocument(RadFlowDocument document, RadFixedDocumentEditor editor)
   at Telerik.Windows.Documents.Flow.FormatProviders.Pdf.Export.PdfExporter.ExportInternal()
   at Telerik.Windows.Documents.Common.FormatProviders.FormatProviderBase`1.Export(T document, Stream output)
   at xxxxx.Application.Common.PdfGeneration.PdfWriter.WriteToPdf(RadFlowDocument document, Stream outputStream) 

        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 });
        }