Is it possible to add additional page to the signed PDF and sign it again without breaking the first signature.
I read in the adobe documentation under incremental updates that it may be possible.
However, I'm not sure if that applies to all the content or just the Annotations (commenting), form fill-in and digital signatures.
I tried to do this by using Apache PDFBox in Java, by signing the document, then loading it, appending the page to it, saving it using saveIncremental() and signing it again.
However, the first signature gets invalidated.
Here is my generateTest method that generates the new PDF:
public byte[] generateTest(InputStream requestPdfIn) throws IOException {
// Create a document and add a page to it
// PDDocument document = new PDDocument();
PDDocument document = PDDocument.load(requestPdfIn);
PDPage page = new PDPage(PDRectangle.A4);
document.addPage(page);
COSBase item = document.getPages().getCOSObject().getItem(COSName.KIDS);
((COSUpdateInfo) item).setNeedToBeUpdated(true);
COSArray kids = (COSArray) item;
kids.setNeedToBeUpdated(true);
((COSUpdateInfo) kids.get(0)).setNeedToBeUpdated(true);
document.getPage(0).getCOSObject().setNeedToBeUpdated(true);
page.getCOSObject().setNeedToBeUpdated(true);
document.getPages().getCOSObject().setNeedToBeUpdated(true);
COSDictionary dict = page.getCOSObject();
while (dict.containsKey(COSName.PARENT)) {
COSBase parent = dict.getDictionaryObject(COSName.PARENT);
if (parent instanceof COSDictionary) {
dict = (COSDictionary) parent;
dict.setNeedToBeUpdated(true);
}
}
document.getDocumentCatalog().getCOSObject().setNeedToBeUpdated(true);
//document.getDocumentCatalog().getStructureTreeRoot().getCOSObject().setNeedToBeUpdated(true);
// Save the results and ensure that the document is properly closed:
ByteArrayOutputStream confirmationPdfOut = new ByteArrayOutputStream();
document.saveIncremental(confirmationPdfOut);
document.close();
return confirmationPdfOut.toByteArray();
}
I found in this post that all the COSObjects need to have a flag needToBeUpdated set to true.
However, that still doesn't help when trying to add another page to the document, as the first signature gets invalidated when I try to verify the signature using Acrobat Reader.
Is it even possible? Is it possible with the PDFBox?
