How Do I Add an eSignature to a PDF Using an API?

There are two approaches depending on whether you need to generate the PDF first or sign an existing one.

Approach 1: Generate the PDF and sign it in one workflow

This is the most efficient approach for teams that create documents from templates — contracts, offer letters, invoices, NDAs, and any document built from structured data.

eSignature API handles both steps in one platform:

1. Create a document template in the drag-and-drop editor
2. Call the API with your data to generate the PDF
3. In the same call, specify recipients and signing fields
4. The API generates the document, adds the fields, and sends it for signing
5. When signing is complete, receive the signed PDF via webhook

This avoids the need for a separate PDF generation tool and a separate signing tool — one API call, one platform, one workflow.

Approach 2: Sign an existing PDF

If you already have a PDF — an uploaded contract, a scanned form, or a document created elsewhere:

1. Upload your PDF as a template or pass the file directly to the API
2. Define where signature fields, date fields, and text fields should appear using x/y coordinates or text tags
3. Specify recipients and signing order
4. Call the API to send for signing
5. Receive the completed signed PDF via webhook

Basic API call example

curl -X POST https://api.craftmypdf.com/v1/create \
  -H "X-API-KEY: your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "template_id": "your_template_id",
    "signers": [
      {
        "name": "Jane Smith",
        "email": "jane@example.com",
        "role": "signer"
      }
    ]
  }'

What happens after signing

• eSignature API sends a webhook POST to your configured URL
• The webhook payload includes document status, signer details, and a download URL
• Download the signed PDF — it includes an embedded audit trail with timestamps, IP addresses, and signing events

Field types you can place on a PDF

eSignature API supports ten field types: signature, initials, date signed, text, checkbox, dropdown, radio button, and more. Fields can be placed precisely using coordinate-based positioning or text tags embedded in the document template.