attach image to fdf using itextsharp - pdf

Question

I'm working to refactor a PDF form web application that is using the Active PDF Toolkit and the FDFToolkit from Adobe. My goal is to use iTextSharp to:
Pre-populate the form fields with data from the database
Allow the user to attach a signature and/or barcode image via FDF
Item #1 is not the problem. Item #2 is the biggest challenge. Let me provide some background:
This is a web application which renders the PDF form once. After the initial load, there are 2 key buttons on the form which submit the PDF form to a URL with an action parameter in the query string. These buttons are called "Save" and "Sign". The Save button takes the FDF field dictionary and saves it to the database. The Sign button looks up the signature for the logged-in user and attaches the signature image to the FDF and writes the FDF to the HTTP Response.
The FDFToolkit supports attaching an image to a field using this method:
FDFSetAP(string bstrFieldName, short whichFace, string bstrFileName, short pageNum)
iTextSharp does not offer a comparable method in the FdfWriter class. I've considered subclassing the FdfWriter class and adding my own method to attach an image, but wanted to reach out here to see if anyone has had the same problem.
I have been able to overlay an image on top of a field using this method, but this is in the underlying PDF and not the FDF.
AcroFields.FieldPosition pos = _Stamper.AcroFields.GetFieldPositions("SIGNATUREFIELD").First();
Image signature = Image.GetInstance("Signature.gif");
image.SetAbsolutePosition(pos.position.Left, pos.position.Bottom);
image.ScaleToFit(pos.position.Width, pos.position.Height);
PdfContentByte pcb = _Stamper.GetOverContent(pos.page);
pcb.AddImage(image);
Thanks!

Answer 1

I've put images on forms by using the PdfStamper and making Pushbutton fields. You can replace your existing field with a Pushbutton field and set the Pushbutton to READ_ONLY so that it can't be pressed and it will look like a static image. This will keep the image you're trying to add as a field annotation instead of adding it to the page content.
using (PdfStamper stamper = new PdfStamper(new PdfReader(inputFile), File.Create(outputFile)))
{
AcroFields.FieldPosition fieldPosition = stamper.AcroFields.GetFieldPositions(fieldName)[0];
PushbuttonField imageField = new PushbuttonField(stamper.Writer, fieldPosition.position, fieldName);
imageField.Layout = PushbuttonField.LAYOUT_ICON_ONLY;
imageField.Image = iTextSharp.text.Image.GetInstance(imageFile);
imageField.ScaleIcon = PushbuttonField.SCALE_ICON_ALWAYS;
imageField.ProportionalIcon = false;
imageField.Options = BaseField.READ_ONLY;
stamper.AcroFields.RemoveField(fieldName);
stamper.AddAnnotation(imageField.Field, fieldPosition.page);
}