Using iTextSharp to write data to PDF works great, but Acrobat Reader asks 'Do you want to save changes' when closing file

Question

I'm using iTextSharp 5.3.2.0 to add information to an existing PDF file that contains a W-2 form. Everything is working perfectly and the PDF file looks great when written into the browser's response stream; however, when the user is done looking at the PDF, he is asked "Do you want to save changes to 'W2.pdf' before closing?" every time he views the document from the web page.

In trying to narrow the problem down, I've actually stripped out all of my modifications but the problem continues. Here's the simple version of my code, with my data-writing call commented out:

PdfReader pdfReader = new PdfReader(dataSource.ReportTemplate);

using(MemoryStream outputStream = new MemoryStream())
using (PdfStamper pdfStamper = new PdfStamper(pdfReader, outputStream))
{
   //dataSource.DrawDataFields(pdfStamper);
   pdfStamper.FormFlattening = true;
   return outputStream;
}

In this case, the "empty" PDF is written to the browser and looks good, but I still get asked, "Do you want to save" when I close the Acrobat window.

At this point I was thinking that there was something wrong with the source PDF file. However, when I send back the PDF file's raw bytes to the browser, I am NOT asked the "Do you want to save" question when using the code below.

byte[] bytes = File.ReadAllBytes(dataSource.ReportTemplate);

using (MemoryStream outputStream = new MemoryStream())
{
    outputStream.Write(bytes, 0, bytes.Length);
    return outputStream;
}

My conclusion is that iTextSharp is doing something "bad" to the PDF in the process of opening it and writing the bytes to the stream, but I'm new to iTextSharp and could easily be missing something.

FWIW, this is Acobat Reader 10.1.4 that we're talking about.

EDIT: The original PDF used as a template is approximately 80K in size. If I look at the temporary file that's been streamed down through my browser, the PDF file written by iTextSharp is approximately 150K. However, when I answer "Yes" to the "Save Changes" question asked by Acrobat Reader, the resulting file is approximately 80K again. iTextSharp is definitely doing something unexpected to this file.

Answer 1

Non-working:

public byte[] MergeDataByDrawing(int copies)
{
    PdfReader pdfReader = new PdfReader(reportTemplate);

    using (MemoryStream outputStream = new MemoryStream())
    using (PdfStamper pdfStamper = new PdfStamper(pdfReader, outputStream))
    {
        pdfStamper.FormFlattening = true;
        return outputStream.GetBuffer();
    }
} 

Working:

public byte[] MergeDataByDrawing(int copies)
{
    PdfReader pdfReader = new PdfReader(reportTemplate);

    using (MemoryStream outputStream = new MemoryStream())
    using (PdfStamper pdfStamper = new PdfStamper(pdfReader, outputStream))
    {
        pdfStamper.FormFlattening = true;
        return outputStream.ToArray();
    }
}

Seems the GetBuffer method is a problem. I don't understand why, but I'll take the result!

Props to MKL for giving me an idea and Fredrik for the right example at the right time.

Answer 2

See http://itextpdf.com/history/?branch=52&node=521

Bugfix AcroForms: In some cases, Adobe Reader X asks if you want to "save changes" after closing a flattened PDF form. This was due to the presence of some unnecessary entries in the /AcroForm dictionary (for instance added when the form was created with OOo).

I'm the Bruno who fixed this bug. I remember that it occurred in Adobe Reader 10, but not in Adobe Reader 9. I was able to fix the bug because the person reporting it was a customer who sent me a PDF that showed this behavior.

If you would share your PDF, we could take a look and see what other entries should be removed from the /AcroForm dictionary. I only removed those that were added when the form is created using Open Office. If you don't want to share the PDF, the cause will always remain a mystery.