Attach an image to an existing PDF at the right position - node.js

Question

So, here's the thing, we have a bunch of pdf forms for users on our website to fill out, we have a submission button inside every pdf form that sends the filled data through a http post method. We are already doing a pre-filled form, where the user fill general information on a html form, data that are used to generate a partially filled multiple pdf files, so whatever the pdf form the user has selected to fill, all of them will be regenerated having the pre-filled information that he just typed on the html form. I accomplish this by using pdftk (http://www.pdflabs.com/docs/pdftk-man-page/) that enables me to just do that. But we get to a point that to make this more efficient, the user must be able to draw their signature on the html side at the pre filled form stage, so we are using signature-pad for this (http://thomasjbradley.ca/lab/signature-pad/), than we create an image from the canvas that the plugin generates. But as each pdf has its own position for the signature, we must insert a placeholder into the pdf that'll be replaced for the signature image. So I came up with the idea to create a disabled text field on the pdf with the name of "signature", so through a nodejs application with the pdf2json module (https://github.com/modesty/pdf2json) I can parse the pdf form and get the position (x,y,w,h) of that particular field, being able to attach an image over the text field placeholder. So the problem is that pdftk don't give me support to attach an image to an existing pdf or even attach it in a certain position, I tried to find a nodejs module that would enables me to do that, but the only worthing nodejs module that I found was pdfkit (http://pdfkit.org/) but it only works creating a new pdf, not editing an exiting one, I looked into pdfkit source code and I discarded it because I realize that it wont work to my case of an existing pdf. So I came to a long way, got to the final stage of this implementation, came to the last step to get this working, and I'm just stack.
This is the output that I have from the pdf2json module for nodejs that is helping with the placeholder approach.
{
page: 7,
index: 317,
name: 'signature',
type: 'alpha',
x: 43.806640625,
y: 14.64195833333333,
w: 30.546828125000005,
h: 1.9339166666666756
}
If someone know any server application that I could run through an unix command at my server to attach an image over an existing pdf document, it'll fit my needs, don't need to be an exclusively nodejs module.
Obs.: I already checked it out the adobe echosign product, but it doesn't fit our needs, it's not free and don't solve our problem of attaching a signature to multiple pdf files from a single html form.

Answer 1

I realize that I could use the nodejs module pdfkit to generate a new blank PDF with the signature in the right position and just over the two pdfs, having the blank pdf with the signature image on the top like a stamp. I could do this with pdftk by command line:
pdftk form.pdf stamp signature.pdf output form-signed.pdf
There's another free application tool like pdftk that I just found out, and it's pdfjam. Also, if you can't use nodejs module pdfkit (different from the application pdfkt) to generate a new pdf with an image to the right spot, you have the stampTK tool (http://www.pdflabs.com/tools/stamptk-the-pdf-stamp-maker/) where you can parse through command line the image to be a stamp in an existing pdf, but this tool is paid (not much, and its worth it), but as I have the pdfkit module for nodejs that enables me to do just that along side the pdfkt application for free, I'm using that, and I also have more control of multiple signatures on the pdfkit module for nodejs. Hope this answer helps someone.