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How to add multiple e-signatures to a pdf via pdfbox and java

I have a pdf signed with a digital certificate. The content of the pdf (form fields) must not be changed after signature. Adding a signature should be allowed. Now a second person needs to add his digital signature. Afterwards no more changes to the document are allowed. How to achieve this?
I was able to create a pdf via java and pdfbox, sign it and check using java that the certificate is valid, that the certificate was used to sign the document.
On stackoverflow I came across the following snippet that adds a signature to a pdf already signed but I don't know how to implement it.
for (int i = 1; i < 4; i++)
{
load current version of the PDF;
apply the i'th signature;
save and sign as new current version of the PDF;
}
I would appreciate advice how to implement the above.

yes, having a look at CreateSignature solved my issue. When I open my document in Acrobat reader now it shows a revision 1, locked against changes by my field signatureField and a certification (by the second signature). In my case the 2nd signature is hidden, but Acrobat reader detects it. Thanks a lot for the help! –

How to create a PDF/DOCX files in Java/Scala?

I am creating a web application which will accept some inputs from user (like name, age, address etc) and generate some predefined forms with filled information for user to download and print.
For example, an Application Form for driving license or something along those lines. The backend will have the format information about the document to be generated and other information will be gathered from user from front-end.
I am going to use Play Framework 2.5 for this and Java/Scala as programming language. But right now I am not aware if there are any free libraries/APIs that I can use to achieve this document generation.
I should be able to manipulate the font size, style, indentations, paragraphs, page borders, page numbers, alignments, document headers and footers, page size (A4, Legal etc) some other basic stuff. And I need documents in format that are widely supported for editing and printing purposes. Like PDF, DOCX for example. DOCX is preferred so user can edit something after downloading the document before taking a print out.

I have used the apache POI library to parse and create ms word documents (including docx) files:
http://www.tutorialspoint.com/apache_poi_word/apache_poi_word_quick_guide.htm
It's not amazing but it's the best I've found :)

I have used docx4j.jar which simply converts xhtml to docx.
What you can do for your requirement is save your format information as xhtml template and place input from form (like name,age,address etc) into the template at runtime.
This is a sample code to refer from this link
public static void main(String[] args) throws Exception
{
String xhtml=
"<table border=\"1\" cellpadding=\"1\" cellspacing=\"1\" style=\"width:100%;\"><tbody><tr><td>test</td><td>test</td></tr><tr><td>test</td><td>test</td></tr><tr><td>test</td><td>test</td></tr></tbody></table>";
// To docx, with content controls
WordprocessingMLPackage wordMLPackage = WordprocessingMLPackage.createPackage();
XHTMLImporterImpl XHTMLImporter = new XHTMLImporterImpl(wordMLPackage);
wordMLPackage.getMainDocumentPart().getContent().addAll(
XHTMLImporter.convert( xhtml, null) );
wordMLPackage.save(new java.io.File("D://sample.docx"));
}

IO Issue - Byte Array Image into XHTML(FlyingSaucer)

I have a solution that inserts strings into an XHTML document and prints the results as Reports. My employer has asked if we could pull images off their SQL database (stored as byte arrays) to insert into the Reports.
I am using FlyingSaucer as the XHTML interpreter and I've been using Java DOM to modify pre-stored reports that I have stored in the Report Generator's package.
The only solution I can think of at the moment is to construct the images, save them as a file, link the file in an img tag (or background-image) in a constructed report, print the report and then delete the file. This seems really sloppy and I imagine it will be very time consuming.
I can't help but feel there must be a more elegant solution. Any suggestions for inserting a byte array into html?

Read the image and convert it into it's Base64-encoded form:
InputStream image = getClass().getClassLoader().getResourceAsStream("image.png");
String encodedImage = BaseEncoding.base64().encode(ByteStreams.toByteArray(image));
I've used BaseEncoding and ByteStreams from Google Guava.
Change src attribute of img element within your Document object.
Document doc = ...; // get Document from XHTMLPanel.getDocument() or create
// new one using DocumentBuilderFactory
doc.getElementById("myImage").getAttributes().getNamedItem("src").setNodeValue("data:image/png;base64," + encodedImage);
Unfortunatley FlyingSaucer does not support DataURIs out-of-the-box so you'll have to create your own ReplacedElementFactory. Read Using Data URLs for embedding images in Flying Saucer generated PDFs article - it contains a complete solution.

Writing to a PDF from inside a GAE app

I need to read several megabytes (raw text strings) out of my GAE Datastore and then write them all to a new PDF file, and then make the PDF file available for the user to download.
I am well aware of the sandbox restrictions that prevent you from writing to the file system. I am wondering if there is a crafty way of creating a PDF in-memory (or a combo of memory and the blobstore) and then storing it somehow so that the client-side (browser) can actually pull it down as a file and save it locally.
This is probably a huge stretch, but my only other option is to farm this task out to a non-GAE server, which I would like to avoid at all cost, even if it takes a lot of extra development on my end. Thanks in advance.

You can definitely achieve your use case using GAE itself. Here are the steps that you should follow at a high level:
Download the excellent iText library, which is a Java library to work with PDFs. First build out your Java code to generate the PDF content. Check out various examples at : http://itextpdf.com/book/toc.php
Since you cannot write to a file directly, you need to generate your PDF content in bytes and then write a Servlet which will act as a Download Servlet. The Servlet will use the Response object to open a stream, manipulate the Mime Headers (filename, filetype) and write the PDF contents to the stream. A browser will automatically present a download option when you do that.
Your Download Servlet will have high level code that looks like this:
public class DownloadPDF extends HttpServlet {
public void doGet(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
//Extract some request parameters, fetch your data and generate your document
String fileName = "<SomeFileName>.pdf";
res.setContentType("application/pdf");
res.setHeader("Content-Disposition", "attachment;filename=\"" + fileName + "\"");
writePDF(<SomeObjectData>, res.getOutputStream());
}
}
}
Remember the writePDF method above is your own method, where you use iText libraries Document and other classes to generate the data and write it ot the outputstream that you have passed in the second parameter.

While I'm not aware of the PDF generation on Google App Engine and especially in Java, but once you have it you can definitely store it and later serve it.
I suppose the generation of the PDF will take more than 30 seconds so you will have to consider using Task Queue Java API for this process.
After you have the file in memory you can simply write it to the Blobstore and later serve it as a regular blob. In the overview you will find a fully functional example on how to upload, write and serve your binary data (blobs) on Google App Engine.

I found a couple of solutions by googling. Please note that I have not actually tried these libraries, but hopefully they will be of help.
PDFJet (commercial)
Write a Google Drive document and export to PDF

How to programatically open a PDF with a User password

This is related to my other question... hope this one has a solution.
The requirement is to display a password-protected PDF in the browser but to pass the User password programatically. I create a PDF using Jasper and set the user password as follows:
exporter.setParameter(JRPdfExporterParameter.USER_PASSWORD, userPassword);
As soon as the PDF is created, it has to be displayed in the screen. While displaying in the browser, the user should not be prompted to key in the password ans hence the password should be supplied by the application However, if the user downloads the PDF and then tries to open it, he should be prompted to enter the password.
[Edit]: I am looking for an approach that does NOT involve licensed tools

You can open a password protected PDF using the PDF.JS library.
PDFJS.getDocument({ url: pdf_url, password: pdf_password }).then(function(pdf_doc) {
// success
}).catch(function(error) {
// incorrect password
// error is an object having 3 properties : name, message & code
});
I've written a blog post on it, also containing a demo. This is the link : http://usefulangle.com/post/22/pdfjs-tutorial-2-viewing-a-password-protected-pdf

I'm not sure whether something of this is possible. On the browser the pdf is opened by a Plugin - usually Adobe Reader plug-in. There are also other makes apart from Adobe Reader. Chrome has it own plugin.
On the browser when it detects any PDF file - the rendering plugin takes over - and this is browser specific. You hardly have any control.
Easy alternative is to show the same content in a web page - probably a modal window if the content is sensitive and give a link to download the password protected pdf file
my 2c

You could checkout PDF.js, an open source client based PDF renderer that also has support for encrypted PDFs.
http://mozilla.github.com/pdf.js/
This means you will have to put your password somewhere in the javascript though, so you will have to disguise it, but it should do the trick :)

You can use pdf.js of mozilla to render password protected PDF. The below url that will prompt for password, until the correct password is given. The password for the pdf is "test".
http://learnnewhere.unaux.com/pdfViewer/passwordviewer.html
Here is the sample code for prompting password
pdfJs.onPassword = function (updatePassword, reason) {
if (reason === 1) { // need a password
var new_password= prompt('Please enter a password:');
updatePassword(new_password);
} else { // Invalid password
var new_password= prompt('Invalid! Please enter a password:');
updatePassword(new_password);
}
};
If you want to close the password prompt on unsuccessful password attempts you can remove the else part(// Invalid password).
You could get the complete code from here https://github.com/learnnewhere/simpleChatApp/tree/master/pdfViewer