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Digital Signatures API

Integrate SOC 2-compliant digital signatures into your apps, websites and platforms. Sign, manage, and validate legally binding documents with ease using our reliable API.

Legally binding and cryptographically secure

Sign PDF documents with digital certificates that meet legal and regulatory standards, no manual steps required.

Built for seamless integration

Use a simple API to sign and validate documents in your own platform or automate it with tools like Zapier, without dealing with complex signature logic or 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 Drive.

Nutrient is used by

Try it out

This example will sign your document with a Nutrient certificate.

1

Use Your Free API Calls

Sign up and receive 100 credits for free, or log in to automatically add your API key to sample code. If you are not sure how credits are consumed read more in our pricing documentation , or check out this guide on calculating credit usage.

Add a File

Add a PDF named document.pdf to your project folder. You can use our sample document. The file name is case sensitive. Make sure the file name matches the file name in the sample code.

Run the Code

Copy the code and run it from the same folder you added the files to. For more information, see our language-specific getting started guides.

View the Results

Open result.pdf in your project folder to view the results.

Important: Signing the document with the free account will use a self-signed certificate. Subscribe to sign with the legally binding certificate.

curl -X POST https://api.nutrient.io/sign \
  -H "Authorization: Bearer your_api_key_here" \
  -o result.pdf \
  --fail \
  -F [email protected] \
  -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 [email protected] ^
  -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.JSONArray;
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 requests
import 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/1.1
Content-Type: multipart/form-data; boundary=--customboundary
Authorization: Bearer your_api_key_here

--customboundary
Content-Disposition: form-data; name="data"
Content-Type: application/json

{
  "signatureType": "cades",
  "cadesLevel": "b-lt"
}
--customboundary
Content-Disposition: form-data; name="file"; filename="document.pdf"
Content-Type: application/pdf

(file data)
--customboundary--
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Your API Key

Security is our top priority

No document storage

No input or resulting documents are stored on our infrastructure. All files are deleted as soon as a request finishes. Alternatively, check out our self-hosted product.

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.

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