public async void ExportAsPDF(string filename, Stream chartStream, SfChart chart)
        {
            NativeChart.SfChart nativeChart = SfChartRenderer.GetNativeObject(typeof(SfChart), chart) as NativeChart.SfChart;

            StorageFolder localFolder = ApplicationData.Current.LocalFolder;
            StorageFile   file        = await localFolder.CreateFileAsync("filename", CreationCollisionOption.ReplaceExisting);

            if (file != null)
            {
                IRandomAccessStream stream = await file.OpenAsync(Windows.Storage.FileAccessMode.ReadWrite);
                await Save_UWP(nativeChart, stream);
            }

            using (var fileStream = await file.OpenAsync(FileAccessMode.Read))
            {
                var reader = new DataReader(fileStream.GetInputStreamAt(0));
                var bytes  = new byte[fileStream.Size];
                await reader.LoadAsync((uint)fileStream.Size);

                reader.ReadBytes(bytes);
                MemoryStream imageStream = new MemoryStream(bytes);

                if (file != null)
                {
                    var       document = new PdfDocument();
                    var       page     = document.Pages.Add();
                    var       graphics = page.Graphics;
                    PdfBitmap image    = new PdfBitmap(imageStream);
                    graphics.DrawImage(image, 0, 0, page.GetClientSize().Width, page.GetClientSize().Height);
                    chartStream = new MemoryStream();
                    document.Save(chartStream);
                    document.Close(true);
                    Save(chartStream, filename, ".pdf");
                }
            }
        }
        public void ExportAsPDF(string filename, Stream chartStream, SfChart chart)
        {
            try
            {
                //Create a new PDF document.
                var document = new PdfDocument();
                var page     = document.Pages.Add();
                var graphics = page.Graphics;
                graphics.DrawImage(PdfImage.FromStream(chartStream), 0, 0, page.GetClientSize().Width, page.GetClientSize().Height);

                MemoryStream stream = new MemoryStream();
                document.Save(stream);
                document.Close(true);
                SavePDF(filename, stream);
            }
            finally
            {
                chartStream.Flush();
                chartStream.Close();

                var nativeChart = SfChartRenderer.GetNativeObject(typeof(SfChart), chart);
                ((Com.Syncfusion.Charts.SfChart)nativeChart).DrawingCacheEnabled = false;
            }
        }