add Digital Signature to pdf with pdfKit and react-signature-canvas for NodeJS / GraphQL

to create hand-craft signature with signaturePad, add date and save to a pdf. then add signature PDF as an additional page attach to the main pdf.

https://www.npmjs.com/package/react-signature-canvas

** need remove alpha from image in order for pdfKit to create pdf by: 
1. set background color to whte

<SignaturePad

ref={sigPad}

backgroundColor="rgba(255,255,255,1)"

canvasProps={{ className: classes.sigPad }}

/>

2. to image/jpeg

const imageData = sigPad.current

.getTrimmedCanvas()

.toDataURL('image/jpeg')

3. merge pdfs using https://www.npmjs.com/package/easy-pdf-merge

export const mergePdfs = async (pdf1: string, pdf2: string, pdf: string) => {

return new Promise((resolve, reject) => {

merge([pdf1, pdf2], pdf, (error: any) => {

if (error) {

return reject(error)

}

resolve('')

})

})

}

====

Here are other ways to sign PDF:

https://www.youtube.com/watch?v=pUIWvJgkw8E

Node Library:

https://www.npmjs.com/package/node-signpdf

import signer from 'node-signpdf';
...
const signedPdf = signer.sign(
  fs.readFileSync(PATH_TO_PDF_FILE)
  fs.readFileSync(PATH_TO_P12_CERTIFICATE),
);