ITextSharp - Adding a Watermark; Leaving the PDF editable - FormFlattening = false - itext

Question

We have a large amount of PDF files that we are creating a web site to allow users to download them and when they do we want to:
Put a watermark on it with their name.
We want the form fields to be left open so they can enter their information.
We want to be able to print and save the document
When I put the Watermark on the document and then open it I get a message from Adobe:
"The document has been changed since it was created and use of extended features is no longer available. Please contact the author..."
According the book "iText-in-Action", this is a security issue (Chapter 8). There seems to be 2 ways to open them:
Remove usage rights : This breaks # 3 above.
Open it in append mode : It does not matter if modify it and save it with "FormFlattening = false" or true, if I put a water mark on the form the fields are no longer editable.
The error message from Adobe does describe the problem, I have modified the content of the document with the watermark, and the form fields become blocked because of this.
I have tried opening the document putting the watermark on it and saving it to a new file, and then closing it. Then reopening it and the trying to unblock the form fields, but it does not work.
Does anyone know if this is possible?
I have read something about templates; I don't know if this is a solution because of the work to convert the documents to templates? Does anyone know if this would help?
Below is a sample of my code for using an Image as a watermark, although I have tried adding text as well:
PdfReader reader = new PdfReader(sourceFile.FullName);
//reader.RemoveUsageRights();
var fileStream = new FileStream(outputPath, FileMode.Create, FileAccess.ReadWrite);
PdfStamper pdfStamper = new PdfStamper(reader, fileStream, '\0', true);
Image image = Image.GetInstance(imagePath);
image.SetAbsolutePosition(250, 300);
for (int i = 1; i <= reader.NumberOfPages; i++) // Must start at 1 because 0 is not an actual page.
{
PdfContentByte pdfPageContents = pdfStamper.GetUnderContent(i);
pdfPageContents.AddImage(image);
}
pdfStamper.FormFlattening = false; // enable this if you want the PDF flattened.
//bool have = pdfStamper.PartialFormFlattening("test");
pdfStamper.Close(); // Always close the stamper or you'll have a 0 byte stream.

Answer 1

A document that is Reader-enabled is digitally signed using a private key owned by Adobe. If Adobe Reader can validate that signature using Adobe's public key, the extra functionality (e.g. allowing you to save a form that has been filled out) is enabled.
Adding a watermark isn't part of the actions you're allowed to do with a digitally signed document. There is absolutely no way you can achieve what you want without invalidating the digital signature that triggers the reader enabling.
In short: you're trying to do something that is impossible. You can only achieve this by using Adobe software because you need Adobe's private key to 'restore' the reader enabling after breaking it.

Answer 2

Good advice.
Every time I reboot my computer Adobe complains about needing to be updated. Last thing I want is to be stuck with a hack, that may not work in the future.
One of my attempts was to create a watermark on a different layer of the PDF in the hopes that it would not see it as changing the text layer of the PDF, but this did not work. My boss had a thought of grabing the text from the original PDF and coping it to a new document and then putting the watermark on it. even though I created a new PDF it still sees it as modifying it, and the fields are still not editable.
Still stuck