Digital signatures API

Use this API for document signing at scale — SOC 2-audited, certificate-based workflows for legally binding electronic signatures. Sign, manage, and validate PDFs in your apps, websites, and platforms using a reliable cloud API.

Legally binding and cryptographically secure

Digitally sign PDF documents with digital certificates that support legal, regulatory, and compliance-oriented workflows aligned with eIDAS and related enterprise signing requirements.

Built for API integration

Use REST, Postman, JavaScript, Python, Java, C#, PHP, or HTTP to sign and validate PDF documents in your own platform without dealing with complex certificate workflows or signing infrastructure.

Try it instantly on Zapier

No code? No problem. Cryptographically sign new PDF files in Google Drive using our Zapier integration, and automatically save the signed copies back to Google Drive.

Used by Lufthansa, Disney, Autodesk, UBS, Dropbox, IBM
Lufthansa
Disney
Autodesk
UBS
Dropbox
IBM

Try it out

This example will sign your document with a Nutrient certificate.


Try it out in three steps

  1. Add a PDF named document.pdf to your project folder.
  2. Run the code from the same folder.
  3. Open result.pdf to see the output.
curl -X POST https://api.nutrient.io/sign \
-H "Authorization: Bearer your_api_key_here" \
-o result.pdf \
--fail \
-F file=@document.pdf \
-F data='{
"signatureType": "cades",
"cadesLevel": "b-lt"
}'

Start now

Create an account to access your API key and start with 50 free credits per month

Start building with DWS Processor API in minutes — no payment information required.

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How does it work?

Obtain the document to be signed

Create signing fields

Collect signer approval

For example, collect ink signatures from all users who need to approve the document before the final digital signature step.


Authenticate

Ensure the correct user is signing the document.


Digitally sign

Use Nutrient’s digital seal (certificate), which guarantees that a document wasn’t tampered with after signing. Tampering with the document in any way invalidates the signature.



Security is our top priority

SOC 2 Type 2 audited

Nutrient’s infrastructure is SOC 2 Type 2 audited and GDPR-compliant. See our privacy policy and security documentation for details on data handling.

HTTPS encryption

All communication between your application and Nutrient is done via HTTPS to ensure your data is encrypted when it’s sent to us.

Safe payment processing

All payments are handled by Paddle. Nutrient DWS Processor API never has direct access to any of your payment data.


Digital signature API questions

What is a digital signature API?

A digital signature API lets you cryptographically sign PDF documents over a REST endpoint instead of building your own certificate and signing infrastructure. Nutrient’s API applies a certificate-based digital seal that guarantees a document wasn’t altered after signing — any change to the file invalidates the signature.

Are signatures created with the API legally binding?

Yes. Signatures are certificate-based and designed for legal, regulatory, and compliance-oriented workflows aligned with eIDAS and related enterprise signing requirements.

Can I build e-signature (electronic signature) workflows with this API?

Yes, with one distinction: this API applies certificate-based digital signatures — the cryptographic seal that makes a signed document tamper-evident and legally binding. For the signer-facing part of an e-signature flow (drawing, typing, or clicking to sign), pair it with Nutrient Web SDK's signing UI; the API then seals the result. Together they cover document signing end to end.

What compliance standards does the digital signature API support?

The API is aligned with eIDAS for certificate-based signing, and the underlying service is SOC 2-audited. For details on data handling and certifications, see the security documentation.

Which programming languages and integrations are supported?

Call the REST API from JavaScript, Python, Java, C#, PHP, or plain HTTP, with a Postman collection available for your first request. For no-code workflows, the Zapier integration can cryptographically sign PDFs from Google Drive automatically.

How do I get started with the digital signature API?

Create a free API key from the dashboard. Then follow the getting started guide. A typical flow is: Obtain the document, create signing fields, collect signer approval, authenticate the signer, and apply the digital signature.

How much does the digital signature API cost?

Signing runs on Nutrient DWS Processor credits. You can start for free, and per-credit rates are listed on the Processor API pricing page.

Can I combine signing with other PDF operations?

Yes. Digital signing is part of the DWS Processor API, so you can chain it with other steps in one workflow — for example, adding password protection and permissions with the PDF security API.

Ready to try it?

Create an account to get your DWS Processor API key and start making API calls.