about visible digital signatures - itext

Question

Given an input pdf file with visible digital signatures, I would like to obtain a new pdf file that preserves the visual representation of the signatures as graphical objects but not longer as signatures fields.
I have done that with a tool (see the input and the output files) but I would like to know how to do it with iText.
input: input.pdf
output: output.pdf

Answer 1

Please be aware that signatures done well (using a certificate from a CA that is member of CDS or AATL) can be verified so that you can test for (1) "integrity", (2) "authentication", and (3) "non-repudiation". By throwing away the signature fields, you lose all that information and nobody will be able to know if the document was changed after signing (1), nor who signed the document (2). The signer can always claim that he never signed that document (3) because anyone could have created the visual representation of his signature.
By removing the signature you will create a copy without an actual signature, similar to what you'd have if you printed a document that is digitally signed. You'll be throwing away important information by removing the actual digital signature, keeping only the visual appearance.
This being said, you are asking for something very simple: you want to flatten a PDF file. This is shown in the FlattenSignature example. Check the file output_no_longer_signed.pdf and you'll notice that it looks exactly like your output.pdf.
The code to achieve this is very simple:
public void manipulatePdf(String src, String dest)
throws DocumentException, IOException {
PdfReader reader = new PdfReader(src);
PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(dest));
stamper.setFormFlattening(true);
stamper.close();
}

Answer 2

For me Bruno's answer didn't work.
I needed to call setGenerateAppearances(true) the be able to see the flattened signatures
public void flatPdf(String src, String dest) throws DocumentException, IOException {
PdfReader reader = new PdfReader(src);
PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(dest));
AcroFields fields = stamper.getAcroFields();
fields.setGenerateAppearances(true);
stamper.setFormFlattening(true);
stamper.close();
}
with: iText 5.5.13