I iterate through the list returned by PDDocumentCatalog.getAcroForm().getFields() and build a new list that does not contain the PDField.findFieldType() == "Sig", then use PDAcroForm.setFields() to have the form use the new field list, or PDDocumentCatalog.setAcroForm( null ) if the new field list is empty.
I also iterate through COSDocument.getSignatureDirectories() and remove them from the document. On Thu, Apr 10, 2014 at 3:49 PM, Ross Woolf <[email protected]> wrote: > As further comment, when I tried to use the method of removing signatures > via deleting the signature fields from the fields array. It first appeared > to work. When the pdf is opened in the adobe reader it does not indicate > anything about signatures and it seems as if none exist, but if I scroll > through the document it will then all of a sudden display a banner that > says that a signature requires validating, but you can't open the signature > panel to investigate. So apparently just removing the signature fields is > not enough. Something remains in the document that causes it to have this > odd behavior. > > Therefore I would like to pursue the approach of removing the incremental > section, but I have no clue how to even find this section or identify it. > Any help would be appreciated. > > -----Original Message----- > From: Ross Woolf > Sent: Wednesday, April 09, 2014 4:31 PM > To: [email protected] > Subject: RE: Validating signatures and removing signatures > > It has been awhile but I am now back on this project. In terms of > removing signatures, I'm interested in the approach of just removing the > incremental section, but being new to PDFBox I am clueless as to how to do > this. Could anyone point me in the direction of how I would go about > finding and removing this section? > > Thanks > > -----Original Message----- > From: Thomas Chojecki [mailto:[email protected]] > Sent: Friday, January 03, 2014 2:37 PM > To: [email protected] > Subject: Re: Validating signatures and removing signatures > > Am Thu, 2 Jan 2014 23:58:51 +0000 > schrieb Ross Woolf <[email protected]>: > > > I have two related questions regarding signed PDF documents > > > > 1. Is it possible with PDFBox to validate signatures? > Not directly. You can extract the cms signature and verify it with bouncy > castle. You can load the document and grab all signatures with > doc.getSignatureDictionaries(). > > The PDSignatureDictionary provides two methods: > 1. byte[] getSignedContent(InputStream pdfFile) This extract the signed > content. The part that the signature covers. > This will extract the Content using the ByteRange. > > 2. byte[] getContents(InputStream pdfFile) With this one you can extract > the signature from the document. This will extract the signature using the > gap declarated by the ByteRange. > > > Next you need to convert the byte[] into a CMS signature object and verify > the signature using the extracted signed content. The certificate can be > extracted from the CMS signature. > > > > 2. Is it possible to remove signatures using PDFBox that were > > previously signed using PDFBox (the same certificate as signing will > > be available)? > Yes, there are two different ways to do that. PDFBox create incremental > updates for each signature. So if you remove the made incremental section, > the document will be exactly the same as before signing. > > The second way is to flatten the document. For this you need to get the > AcroForms from the Catalog and remove the SignatureField from the Fields > array. > > PDDocumentCatalog catalog = doc.getDocumentCatalog(); PDAcroForm acroform > = catalog.getAcroForm(); List fields = acroform.getFields(); > > Now you need to find the right signature field and remove it from the > document. I did not know if this work properly, some people on the > mailinglist means, this method does not work. > > > But if you just add new content and sign it again, you can leave the > signatures where it is. The signature covers only a specific part of the > document and does not break if new content will be add incremental. At the > moment the pdfbox only support incremental updates for signature. If you > want to add additional content like pages, you will break the signature if > you save the document the convetional way. > > If you add a new page and add a signature,this maybe will work. I've don't > test it yet. > > > For integrity sake before appending the pages I want to check that the > > original signature is valid, and if so, then remove the original > > signature, append the necessary data, and then sign the document anew > > relative to the modified document and then send it on to the > > requester. > > Try the last made sugestion with adding a page and signature and perform a > saveIncremental. > > Best regards > Thomas >
