[NodeJs] RSA Digital signature to PDF file with QRCODE

index.js

const fs = require('fs');
const qrcode = require('qrcode');
const { rsa, rsaSign } = require('crypsi');
const { PDFDocument } = require('pdf-lib');
const main = () => {
    return new Promise((resolve, reject) => {
        const privateKeyData = fs.readFileSync('private_key_pkcs8.key');
        const publicKeyData = fs.readFileSync('public.key');
        
        const pdfBuffer = fs.readFileSync('pdf_file.pdf');

        // sign pdf file
        const signature = rsaSign.
            signWithPSSSha256(rsa.loadPrivateKey(privateKeyData), pdfBuffer);
        
        // save signature to database
        console.log(signature);

        // create short version of signature
        const signatureShort = signature.substring(0, 40);
        console.log(signatureShort);

        // append with your verification routes HTTP REST API
        const apiURL = 'https://api.yoursite.com/verify-signature';

        // create qr code
        qrcode.toBuffer(`${apiURL}/${signatureShort}`, async (err, qrData) => {
            
            if (err) {
                reject(err);
                return;
            }

            try {
                const pdfDoc = await PDFDocument.load(pdfBuffer);
                const firstPage = pdfDoc.getPages()[0];

                // Get the width and height of the first page
                const { width, height } = firstPage.getSize();

                const qrImage = await pdfDoc.embedPng(qrData);
                const qrDims = qrImage.scale(0.5);
                firstPage.drawImage(qrImage, {
                    x: 25,
                    y: 25,
                    width: qrDims.width,
                    height: qrDims.height,
                    opacity: 0.90,
                });

                const pdfBufferOutput = await pdfDoc.save();
                fs.writeFile('pdf_file_out.pdf', pdfBufferOutput, 'binary', (err) => {
                    if (err) {
                        reject(err);
                        return;
                    }

                    resolve('ok');
                });
            } catch(e) {
                reject(r);
                return;
            }
        });
    });
};

main().then(r => console.log(r)).catch(e => console.log(e));

dependencies:

npm install --save qrcode
npm install --save pdf-lib
npm install --save crypsi