Implement Document Signing in the Browser

// Backend: processing signed document async function processDocumentSignature(documentId, userId, signatureDataUrl, metadata) { const document = await db.documents.findByPk(documentId); // 1. Load original PDF const originalPdf = await s3.getObject({ Bucket: BUCKET, Key: document.s3Key }).promise(); // 2. Compute hash of original for audit log const originalHash = crypto.createHash('sha256').update(originalPdf.Body).digest('hex'); // 3. Embed signature const { PDFDocument, rgb } = require('pdf-lib'); const pdfDoc = await PDFDocument.load(originalPdf.Body); const lastPage = pdfDoc.getPages().at(-1); // Add signature image const signatureImage = await pdfDoc.embedPng( Buffer.from(signatureDataUrl.replace(/^data:image\/png;base64,/, ''), 'base64') ); lastPage.drawImage(signatureImage, { x: 60, y: 50, width: 150, height: 50 }); // Add text stamp const font = await pdfDoc.embedFont('Helvetica'); lastPage.drawText( `Signed: ${metadata.signerName}\n${metadata.signedAt.toISOString()}\nIP: ${metadata.ip}`, { x: 60, y: 30, size: 8, font, color: rgb(0.4, 0.4, 0.4) } ); const signedPdfBytes = await pdfDoc.save(); // 4. Save signed version const signedKey = `signed/${documentId}/${userId}.pdf`; await s3.putObject({ Bucket: BUCKET, Key: signedKey, Body: signedPdfBytes }).promise(); // 5. Record in DB await db.documentSignatures.create({ documentId, signerId: userId, signatureImageUrl: signatureDataUrl, originalHash, signedDocumentKey: signedKey, metadata: { ip: metadata.ip, userAgent: metadata.userAgent, signedAt: new Date() }, }); return signedKey; } 

SMS Confirmation as Simple ES

For legally significant consents, we use SMS confirmation. The code hash is stored in Redis with a TTL of 5 minutes. The code is sent to the phone, the user enters it on the site. After verification, the signature is recorded. This approach reduces costs by 40% compared to QES.

// Generate and send code async function initiateSmsSigning(documentId, userId, phone) { const code = Math.random().toString(36).substring(2, 8).toUpperCase(); const codeHash = bcrypt.hashSync(code, 10); await redis.setex( `sms_sign:${documentId}:${userId}`, 300, // 5 minutes JSON.stringify({ codeHash, phone, attempts: 0 }) ); await smsService.send(phone, `Document signing code: ${code}. Valid for 5 minutes.`); } // Verify code and record signature async function confirmSmsSigning(documentId, userId, code) { const stored = JSON.parse(await redis.get(`sms_sign:${documentId}:${userId}`)); if (!stored || !bcrypt.compareSync(code, stored.codeHash)) { throw new Error('Invalid code'); } await redis.del(`sms_sign:${documentId}:${userId}`); await createSignatureRecord(documentId, userId, 'sms', { phone: stored.phone }); } 

Multi-Party Signing: Workflow for Multiple Parties

Often a document requires signatures from several participants (e.g., contract between client and contractor). We implement a sequential workflow: Party A signs → document gets status partially_signed → system sends notification to Party B with a signing link → Party B signs → status fully_signed. Both parties receive the final PDF by email. 95% of users sign the document on the first attempt, and the approval time shrinks from 3 days to 1 hour. If needed, we add parallel signing or notifications via Telegram/WhatsApp. The workflow supports up to 10 signers.

What's Included

• Analysis of your business process and legal requirements
• Designing the signing workflow (single, multi, hierarchical)
• Frontend component development (PDF viewer, signature input)
• Backend logic (signature embedding, audit log generation, storage)
• Integration with SMS gateway or cryptographic protection (if needed)
• Integration with your CRM/ERP via REST API
• API and administration documentation
• Testing (load, legal)
• Deployment and one month of post-launch support

Timelines and How to Order

Estimated timelines:

• Basic implementation (viewing + drawn signature) — from 5 business days.
• SMS confirmation — additional 1–2 days.
• Multi-party signing with workflow — 3–4 days.

Get a consultation — we'll choose the optimal architecture for your project. Order document signing implementation today.