private void pdfViewer1_MouseDoubleClick(object sender, MouseButtonEventArgs e)
{
    //Determine the page where the mouse was clicked
    int pageNum = pdfViewer1.PointInPage(e.GetPosition(pdfViewer1));
    var page = pdfViewer1.Document.Pages[pageNum];
    //Translate the mouse coordinates to the page's coordinate system
    var pointOnPage = pdfViewer1.ClientToPage(pageNum, e.GetPosition(pdfViewer1));
    //Load bitmap from file, create image object and insert it into page
    var bmp = PdfBitmap.FromFile(@"d:\0\img1.png");
    var imageObj = PdfImageObject.Create(pdfViewer1.Document, bmp, (float)pointOnPage.X, (float)pointOnPage.Y);
    page.PageObjects.Add(imageObj);
    //Generate page content 
    page.GenerateContent();
    //And invalidate 
    pdfViewer1.ClearRenderBuffer();
    pdfViewer1.InvalidateVisual();
    //Save document
    pdfViewer1.Document.Save(@"d:\0\6\test.pdf", SaveFlags.NoIncremental);
}