using Patagames.Pdf.Enums;
using Patagames.Pdf.Net;
using Patagames.Pdf;
using Patagames.Pdf.Net.BasicTypes;

private void pdfViewer1_MouseDoubleClick(object sender, MouseEventArgs e)
{
    //Determine the page number where the mouse was clicked
    int page = pdfViewer1.PointInPage(e.Location);
    //( e.GetPosition(pdfViewer1));
    //Translate the mouse coordinates to the page's coordinate system
    var pointOnPage = pdfViewer1.ClientToPage(page, e.Location);
        //GetPosition(pdfViewer1));
    //Load bitmap from file and insert it into page
    var bmp = System.Drawing.Bitmap.FromFile(@"C:\test.png") as System.Drawing.Bitmap;
    var image = InsertImageToPage(pdfViewer1.Document, pdfViewer1.Document.Pages[page], bmp, pointOnPage);
    pdfViewer1.ClearRenderBuffer();
    pdfViewer1.Invalidate();
            
    //InvalidateVisual();
    //Insert image into page dictionary
    InsertIntoDictionary(pdfViewer1.Document, pdfViewer1.Document.Pages[page], image);
    //Save document
    pdfViewer1.Document.Save(@"C:\test2.pdf", SaveFlags.NoIncremental);

}

public PdfImageObject InsertImageToPage(PdfDocument doc, PdfPage page, System.Drawing.Bitmap bmp, PointF atPoint)
{
    var bi = bmp.LockBits(
        new System.Drawing.Rectangle(0, 0, bmp.Width, bmp.Height),
        System.Drawing.Imaging.ImageLockMode.ReadOnly,
        System.Drawing.Imaging.PixelFormat.Format32bppArgb);

    //Create PdfBitmap object from .Net bitmap
    var bitmap = new PdfBitmap(
        bmp.Width,
        bmp.Height,
        BitmapFormats.FXDIB_Argb,
        bi.Scan0,
        bi.Stride);

    //Create pdf image object and then set PdfBitmap object into it.
    var image = PdfImageObject.Create(doc);
    image.SetBitmap(bitmap);

    //Scale image object to it's actual width and heihgt
    image.SetMatrix(bmp.Width, 0, 0, bmp.Height, (float)atPoint.X, (float)atPoint.Y);

    page.PageObjects.InsertObject(image);
    return image;
}

public void InsertIntoDictionary(PdfDocument doc, PdfPage page, PdfImageObject image)
{
    //Get page dictionary, list of indirect objects and original page content
    var pageDict = page.Dictionary;
    var list = PdfIndirectList.FromPdfDocument(doc);

    //Convert contents to array. 
    PdfTypeArray array = ConvertContentsToArray(pageDict["Contents"], list, pageDict);

    //Get stream of image.
    IntPtr streamHandle = Pdfium.FPDFImageObj_GenerateStream(image.Handle, page.Handle);
    var stream = PdfTypeStream.Create(streamHandle);

    //Add image's stream into list of indirect objects and then add it to array.
    int num = list.Add(stream);
    array.AddIndirect(list, num);
}

public PdfTypeArray ConvertContentsToArray(PdfTypeBase contents, PdfIndirectList list, PdfTypeDictionary pageDict)
{
    //check the original content whether it's an array
    if (contents is PdfTypeArray)
        return contents as PdfTypeArray;  //if contents is a array just return it
    else if (contents is PdfTypeIndirect)
    {
        if ((contents as PdfTypeIndirect).Direct is PdfTypeArray)
            return (contents as PdfTypeIndirect).Direct as PdfTypeArray; //if contents is a reference to array then return that array
        else if ((contents as PdfTypeIndirect).Direct is PdfTypeStream)
        {
            //if contents is a reference to a stream then create a new array and insert stream as a first element of array
            var array = PdfTypeArray.Create();
            array.AddIndirect(list, (contents as PdfTypeIndirect).Direct);
            //Add array into list of indirect objects
            list.Add(array);
            //And set it as a contents of the page
            pageDict.SetIndirectAt("Contents", list, array);
            return array;
        }
        else
            throw new Exception("Unexcpected content type");
    }
    else
        throw new Exception("Unexcpected content type");
}