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.
Digitally sign PDF documents with digital certificates that support legal, regulatory, and compliance-oriented workflows aligned with eIDAS and related enterprise signing requirements.
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.
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.
This example will sign your document with a Nutrient certificate.
Try it out in three steps
document.pdf to your project folder.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" }'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\"}"package com.example.pspdfkit;
import java.io.File;import java.io.IOException;import java.nio.file.FileSystems;import java.nio.file.Files;import java.nio.file.StandardCopyOption;
import org.json.JSONObject;
import okhttp3.MediaType;import okhttp3.MultipartBody;import okhttp3.OkHttpClient;import okhttp3.Request;import okhttp3.RequestBody;import okhttp3.Response;
public final class PspdfkitApiExample { public static void main(final String[] args) throws IOException { final RequestBody body = new MultipartBody.Builder() .setType(MultipartBody.FORM) .addFormDataPart( "file", "document.pdf", RequestBody.create( MediaType.parse("application/pdf"), new File("document.pdf") ) ) .addFormDataPart( "data", new JSONObject() .put("signatureType", "cades") .put("cadesLevel", "b-lt").toString() ) .build();
final Request request = new Request.Builder() .url("https://api.nutrient.io/sign") .method("POST", body) .addHeader("Authorization", "Bearer your_api_key_here") .build();
final OkHttpClient client = new OkHttpClient() .newBuilder() .build();
final Response response = client.newCall(request).execute();
if (response.isSuccessful()) { Files.copy( response.body().byteStream(), FileSystems.getDefault().getPath("result.pdf"), StandardCopyOption.REPLACE_EXISTING ); } else { // Handle the error throw new IOException(response.body().string()); } }}using System;using System.IO;using System.Net;using RestSharp;
namespace PspdfkitApiDemo{ class Program { static void Main(string[] args) { var client = new RestClient("https://api.nutrient.io/sign");
var request = new RestRequest(Method.POST) .AddHeader("Authorization", "Bearer your_api_key_here") .AddFile("file", "document.pdf") .AddParameter("data", new JsonObject { ["signatureType"] = "cades", ["cadesLevel"] = "b-lt" }.ToString());
request.AdvancedResponseWriter = (responseStream, response) => { if (response.StatusCode == HttpStatusCode.OK) { using (responseStream) { using var outputFileWriter = File.OpenWrite("result.pdf"); responseStream.CopyTo(outputFileWriter); } } else { var responseStreamReader = new StreamReader(responseStream); Console.Write(responseStreamReader.ReadToEnd()); } };
client.Execute(request); } }}// This code requires Node.js. Do not run this code directly in a web browser.
const axios = require('axios')const FormData = require('form-data')const fs = require('fs')
const formData = new FormData()formData.append('data', JSON.stringify({ signatureType: "cades", cadesLevel: "b-lt"}))formData.append('file', fs.createReadStream('document.pdf'))
;(async () => { try { const response = await axios.post('https://api.nutrient.io/sign', formData, { headers: formData.getHeaders({ 'Authorization': 'Bearer your_api_key_here' }), responseType: "stream" })
response.data.pipe(fs.createWriteStream("result.pdf")) } catch (e) { const errorString = await streamToString(e.response.data) console.log(errorString) }})()
function streamToString(stream) { const chunks = [] return new Promise((resolve, reject) => { stream.on("data", (chunk) => chunks.push(Buffer.from(chunk))) stream.on("error", (err) => reject(err)) stream.on("end", () => resolve(Buffer.concat(chunks).toString("utf8"))) })}import requestsimport json
response = requests.request( 'POST', 'https://api.nutrient.io/sign', headers = { 'Authorization': 'Bearer your_api_key_here' }, files = { 'file': open('document.pdf', 'rb') }, data = { 'data': json.dumps({ 'signatureType': 'cades', 'cadesLevel': 'b-lt' }) }, stream = True)
if response.ok: with open('result.pdf', 'wb') as fd: for chunk in response.iter_content(chunk_size=8096): fd.write(chunk)else: print(response.text) exit()<?php
$FileHandle = fopen('result.pdf', 'w+');
$curl = curl_init();
curl_setopt_array($curl, array( CURLOPT_URL => 'https://api.nutrient.io/sign', CURLOPT_CUSTOMREQUEST => 'POST', CURLOPT_RETURNTRANSFER => true, CURLOPT_ENCODING => '', CURLOPT_POSTFIELDS => array( 'data' => '{ "signatureType": "cades", "cadesLevel": "b-lt" }', 'file' => new CURLFILE('document.pdf') ), CURLOPT_HTTPHEADER => array( 'Authorization: Bearer your_api_key_here' ), CURLOPT_FILE => $FileHandle,));
$response = curl_exec($curl);
curl_close($curl);
fclose($FileHandle);POST https://api.nutrient.io/sign HTTP/1.1Content-Type: multipart/form-data; boundary=--customboundaryAuthorization: Bearer your_api_key_here
--customboundaryContent-Disposition: form-data; name="data"Content-Type: application/json
{ "signatureType": "cades", "cadesLevel": "b-lt"}--customboundaryContent-Disposition: form-data; name="file"; filename="document.pdf"Content-Type: application/pdf
(file data)--customboundary--For example, collect ink signatures from all users who need to approve the document before the final digital signature step.
Ensure the correct user is signing the document.
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.
Most common next steps
Use the following:
Get started:
Platform resources:
Nutrient’s infrastructure is SOC 2 Type 2 audited and GDPR-compliant. See our privacy policy and security documentation for details on data handling.
All communication between your application and Nutrient is done via HTTPS to ensure your data is encrypted when it’s sent to us.
All payments are handled by Paddle. Nutrient DWS Processor API never has direct access to any of your payment data.
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.
Yes. Signatures are certificate-based and designed for legal, regulatory, and compliance-oriented workflows aligned with eIDAS and related enterprise signing requirements.
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.
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.
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.
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.
Signing runs on Nutrient DWS Processor credits. You can start for free, and per-credit rates are listed on the Processor API pricing page.
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.
Create an account to get your DWS Processor API key and start making API calls.