How to print the document contents of SfRichTextBoxAdv control by retrieving document pages as Image?

// Initializes a list of BitmapImage to store images of pages.
List<BitmapImage> pageImages = new List<BitmapImage>();
 
// Gets the page images asynchronously.
async Task<bool> GetPageImagesAsync()
{
    TaskCompletionSource<bool> taskCompletionSource = new TaskCompletionSource<bool>();
    // Clears the page images.
    pageImages.Clear();
    int pageCount = richTextBoxAdv.PageCount;
    for (int i = 0; i < pageCount; i++)
    {
        // Retrieve page in RichTextBoxAdv as BitmapImage by specifying page number.
        BitmapImage bitmapImage = await richTextBoxAdv.GetPageAsImageAsync(i);
        pageImages.Add(bitmapImage);
    }
    taskCompletionSource.SetResult(true);
    return await taskCompletionSource.Task;
}

// Initializes PrintDocument instance.
PrintDocument printDocument = new PrintDocument();
IPrintDocumentSource printDocumentSource;
 
// Registers for Printing
void RegisterForPrinitng()
{
    // Hooks print task requested event handler.
    PrintManager printManager = PrintManager.GetForCurrentView();
    printManager.PrintTaskRequested += PrintManager_PrintTaskRequested;
 
    // Initializes the print document source.
    printDocumentSource = printDocument.DocumentSource;
 
    // Hooks print document event handlers.
    printDocument.Paginate += PrintDocument_Paginate;
    printDocument.GetPreviewPage += PrintDocument_GetPreviewPage;
    printDocument.AddPages += PrintDocument_AddPages;
}
 
// Print Task Requested event handler
private void PrintManager_PrintTaskRequested(PrintManager sender, PrintTaskRequestedEventArgs args)
{
    PrintTask printTask = null;
    printTask = args.Request.CreatePrintTask("Document", sourceRequested =>
    {
        // Prints Task event handler invoked when the print job is completed.
        printTask.Completed += PrintTask_Completed;
        sourceRequested.SetSource(printDocumentSource);
    });
}
 
// Print Task Completed Event Handler
private void PrintTask_Completed(PrintTask sender, PrintTaskCompletedEventArgs args)
{
    pageImages.Clear();
}
 
// Print Document Paginate event handler.
private void PrintDocument_Paginate(object sender, PaginateEventArgs e)
{
    int pageCount = richTextBoxAdv.PageCount;
    PrintDocument printDocument = sender as PrintDocument;
    // Report the number of preview pages created.
    printDocument.SetPreviewPageCount(pageCount, PreviewPageCountType.Intermediate);
}
 
// Print Document Get Preview Page event handler.
private void PrintDocument_GetPreviewPage(object sender, GetPreviewPageEventArgs e)
{
    PrintDocument printDocument = sender as PrintDocument;
    int currentPreviewPage = 0;
    Interlocked.Exchange(ref currentPreviewPage, e.PageNumber - 1);
    if (pageImages.Count >= e.PageNumber)
    {
        BitmapImage bitmap = pageImages[e.PageNumber - 1];
        Image image = new Image();
        image.Source = bitmap;
        printDocument.SetPreviewPage(e.PageNumber, image);
    }
}
 
// Print Document Add Pages event handler.
private void PrintDocument_AddPages(object sender, AddPagesEventArgs e)
{
    int pageCount = richTextBoxAdv.PageCount;
    for (int i = 0; i < pageImages.Count; i++)
    {
        Image image = new Image();
        image.Source = pageImages[i];
        printDocument.AddPage(image);
    }
    printDocument.AddPagesComplete();
}

// Invokes printing asynchronously.
async void InvokePrintAsync()
{
    bool pagesRetrieved = await GetPageImagesAsync();
    if (pagesRetrieved)
        await PrintManager.ShowPrintUIAsync();
}

// Unregisters printing.
void UnRegisterPrinting()
{
    // Unhooks the print document event handlers.
    if (printDocument != null)
    {
        printDocument.Paginate -= PrintDocument_Paginate;
        printDocument.GetPreviewPage -= PrintDocument_GetPreviewPage;
        printDocument.AddPages -= PrintDocument_AddPages;
        printDocumentSource = null;
        printDocument = null;
    }
    // Unhooks the print task requested event handler.
    PrintManager printManager = PrintManager.GetForCurrentView();
    printManager.PrintTaskRequested -= PrintManager_PrintTaskRequested;
}