Unable to save a valid version of the signed PDF file

[radoslavpetranov]

Describe the bug and the expected behaviour Here is a test function that I use to test signing a dummy PDF document with a dummy certificate.

export const testFileSigning = (_req: Request, res: Response, next: NextFunction) => {

  // Hardcode some paths for testing purposes
  const pdfFilePath = "c:/temp/cert/cert.pdf";
  const pdfSignedFilePath = "c:/temp/cert/cert_signed.pdf";
  const certFilePath = "c:/temp/cert/certificate.p12";

  // Create some streams
  const p12Buffer = fs.readFileSync(certFilePath);
  let pdfBuffer = fs.readFileSync(pdfFilePath);

  // Add placeholder
  pdfBuffer = plainAddPlaceholder.default({
    pdfBuffer,
    reason: 'I have reviewed it.',
    signatureLength: 8192,
  });
  try {
    // Sign the doc
    pdfBuffer = signer.sign(pdfBuffer, p12Buffer);
  } catch (err) {
    console.error(`Error signing document`, err);
    next(err);
  }

  // Write to file
  fs.writeFile(pdfSignedFilePath, pdfBuffer, { encoding: 'binary' }, (err) => {
    if (!!err) {
      next(err);
    } else {
      res.locals.data = { signed: true };
      next();
    }
  });
};

So fs.writeFile saves the pdfBuffer that results from the sign method into a file called cert_signed.pdf.

When I open the file, the file is blank, it's broken / tiny so that it's zoomed in to like 4000%

and when I try to zoom out I see that error

There was a problem reading this document (14)

and the file itself seems to be corrupt / empty.

Is it a bug in signing or in the helpers? I am not even sure if this is a bug or if I'm doing something wrong when trying to save the signed file. If it's a bug I would assume it's a bug with the sign function.

To Reproduce I've described how to reproduce the issue in the previous points. I am testing with the certificate.p12 file that comes in this repo. I have also attached the 2 PDF files: the source cert.pdf file as well as the resulting cert_signed.pdf file.

cert.pdf cert_signed.pdf

Your help would be appreciated. I saw someone else pointing to this error in a closed github issue so I figured I would make a separate issue for anyone facing the same problem as me.

[radoslavpetranov]

Interestingly enough, here's what the cert_signed.pdf file looks like in chrome

and here what it looks like in Adobe Acrobat Reader DC

[vbuch]

In the resulting PDF I see

<<

/Type /Catalog
/Pages 1 0 R

/AcroForm 17 0 R
>>
endobj

6 0 obj
<<
 16 0 R]
/Contents 4 0 R
/Resources 5 0 R

>>
endobj

This looks wrong. Not sure what got broken there without going through code. What version are you using? Is it 1.2.2?

Object 6 was the page. In the original document it was OK. After signing, it's crappy. Save the pdfBuffer after plainAddPlaceholder so we can confirm if the issue is in it.

[radoslavpetranov]

Thanks for looking into this! Yes, I am using version 1.2.2.

Here's the updated code that saves the file after adding the placeholder

// Hardcode some paths for testing purposes
const pdfFilePath = "c:/temp/cert/cert.pdf";
const pdfWithPlaceholderFilePath = "c:/temp/cert/cert_placeholder.pdf";

// Create some streams
let pdfBuffer = fs.readFileSync(pdfFilePath);

// Add placeholder
pdfBuffer = plainAddPlaceholder.default({
  pdfBuffer,
  reason: 'I have reviewed it.',
  signatureLength: 8192,
});
fs.writeFile(pdfWithPlaceholderFilePath, pdfBuffer, { encoding: 'binary' }, (err) => {
  if (!!err) {
    next(err);
  } else {
    res.locals.data = { signed: true };
    next();
  }
});

And the resulting file is attached.

cert_placeholder.pdf

[vbuch]

OK. Confirmed. It's an issue with plainAddPlaceholder. The page object gets broken through it. Would love it if you can make a PR with a fix. Otherwise you'll have to wait as I don't have the time to debug it.

[radoslavpetranov]

I'm no PDF expert but I'll see if I can figure out what's going on.

I just used a hex editor and I confirm that if I change the broken obj part from

6 0 obj
<<
 16 0 R]
/Contents 4 0 R
/Resources 5 0 R

>>
endobj

to

6 0 obj
<<
/Type /Page
/Parent 1 0 R
/MediaBox [0 0 595.28 841.89]
/Contents 4 0 R
/Resources 5 0 R
>>
endobj

the file gets properly rendered

[vbuch]

And this resulting one you will be able to sign. The problem is somewhere in plainaddplaceholder. Somewhere where this /type /page object is written back in the pdf. Probably around here: https://github.com/vbuch/node-signpdf/blob/develop/src/helpers/plainAddPlaceholder/createBufferPageWithAnnotation.js

[vbuch]

@radoslavpetranov (now that I wrote your name I am pretty sure you are also a Bulgarian :-)) Can try and check the code in #59 I will get this to 1.2.3 later today but if you could confirm meanwhile, would be really nice. Thanks.

[radoslavpetranov]

Guilty as charged :)

I just tested your changes and everything works great now! Thanks a lot for figuring this out!!

[vbuch]

Have not released yet. Just merged into develop.

[vbuch]

1.2.3 is out in npm. Hope it fixes this issue.