private static async Task<string> RenderPage(Windows.Data.Pdf.PdfPage page, StorageFolder output)
        {
            var pagePath = string.Format("{0}.png", page.Index);
            var pageFile = await output.CreateFileAsync(pagePath, CreationCollisionOption.ReplaceExisting);
            
            using (var imageStream = await pageFile.OpenAsync(FileAccessMode.ReadWrite))
            {
                PdfPageRenderOptions pdfPageRenderOptions = new PdfPageRenderOptions();
                pdfPageRenderOptions.IsIgnoringHighContrast = false;
                await page.RenderToStreamAsync(imageStream, pdfPageRenderOptions);
                await imageStream.FlushAsync();
            }

            return output.Path.ToFolderPath() + pagePath;
        }