How do I make an image not selectable - vb.net

Question

I have added an image to my iTextSharp PDF document like this:
Public Sub CreatePDFFromBitmap(ByVal uPath As String, ByVal uBitmap As Bitmap)
Dim nFs As System.IO.FileStream = New FileStream(uPath, FileMode.Create)
Dim nDocument As iTextSharp.text.Document
Dim nWriter As iTextSharp.text.pdf.PdfWriter
Dim nCb As iTextSharp.text.pdf.PdfContentByte
Dim nImgFromBitmap As System.Drawing.Image = DirectCast(uBitmap, System.Drawing.Image)
Dim nImg As iTextSharp.text.Image = iTextSharp.text.Image.GetInstance(nImgFromBitmap, Imaging.ImageFormat.Png)
Dim bLandscape As Boolean = (nImg.Width > nImg.Height)
'rotation needs to be set before document is being opened
If bLandscape Then
nDocument = New iTextSharp.text.Document(PageSize.A4.Rotate, 0, 0, 0, 0)
Else
nDocument = New iTextSharp.text.Document(PageSize.A4, 0, 0, 0, 0)
End If
'if an exception is raised here, the following will help: https://stackoverflow.com/questions/15833285/pdfwriter-getinstance-throws-system-nullreferenceexception
nWriter = iTextSharp.text.pdf.PdfWriter.GetInstance(nDocument, nFs)
nDocument.Open()
nCb = nWriter.DirectContent
nImg.ScaleToFit(nDocument.PageSize.Width, nDocument.PageSize.Height) 'raises dpi size :-)))
'X-Y-Koordinatensystem 0,0 startet also unten links, nicht oben-links
nImg.SetAbsolutePosition(0, nDocument.PageSize.Height - nImg.ScaledHeight)
nCb.AddImage(nImg)
nDocument.Close()
nWriter.Close()
nFs.Close()
End Sub
It works fine.
However, when I click the image in the PDF, it gets selected.
This is not what I want.
If I click the image in the PDF, it should not be selected.
This is what it looks like: The image becomes blue:
I want to add editable fields to the PDF, so I need to make the image not selectable, else it would confuse the user.

Answer 1

As Abdel-Rahman Al-Qawasmi mentions in his answer, it is completely up to the PDF viewer which entities it makes selectable and which not. Thus, there is no guaranteed way to get what you want.
Nonetheless, there are ways to put an image into a PDF which dissuade current versions of most PDF viewers from making it selectable. These ways either transform the bitmap image into a non-bitmap entity (e.g. by iterating over the pixels of the bitmap and drawing a little rectangle per pixel using vector graphics) or wrap the bitmap image into something that usually is not selectable.
Let's take the latter approach and wrap the image into a page-size PDF pattern with which we then fill the actual page. You can do that by replacing your
nCb.AddImage(nImg)
by
Dim painter As iTextSharp.text.pdf.PdfPatternPainter = nCb.CreatePattern(nDocument.PageSize.Width, nDocument.PageSize.Height)
painter.AddImage(nImg)
nCb.SetColorFill(New iTextSharp.text.pdf.PatternColor(painter))
nCb.Rectangle(0, 0, nDocument.PageSize.Width, nDocument.PageSize.Height)
nCb.Fill()
(This essentially is the VB/iTextSharp pendant of the Java/iText code from this answer.)

Answer 2

This is a pdf program specifications and not related to asp.net or vb.net programming. you need to have control of the pdf reader settings. Or try to use another format.