---
title: "API overview"
canonical_url: "https://www.nutrient.io/guides/dws-processor/developer-guides/"
md_url: "https://www.nutrient.io/guides/dws-processor/developer-guides.md"
last_updated: "2026-05-27T21:01:12.682Z"
description: "Learn how to use Nutrient DWS Processor API to assemble PDF documents from multiple parts using HTTP requests."
---

# API overview

Nutrient DWS Processor API exposes a single HTTP endpoint for usage:

```

POST https://api.nutrient.io/build

```

This endpoint enables you to declaratively assemble a PDF document from multiple independent parts, applying actions on the whole output file and single parts.

The API expects data to be sent either as as `multipart/form-data` or `application/json` content types.

## Multipart request

The basic use case for the `/build` API is to upload all inputs together with the processing instructions with the `multipart/form-data` request:

### Shell

```shell

curl -X POST https://api.nutrient.io/build \
  -H "Authorization: Bearer your_api_key_here" \
  -o result.pdf \
  --fail \
  -F document=@input-file.pdf \
  -F instructions='{
      "parts": [
        {
          "file": "document"
        }
      ],
      "actions": [
        {
          "type": "flatten"
        }
      ]
    }'

```

### Shell (Windows)

```powershell

curl -X POST https://api.nutrient.io/build ^
  -H "Authorization: Bearer your_api_key_here" ^
  -o result.pdf ^
  --fail ^
  -F document=@input-file.pdf ^
  -F instructions="{\"parts\": [{\"file\": \"document\"}], \"actions\": [{\"type\": \"flatten\"}]}"

```

### Java

```java

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(
        "document",
        "input-file.pdf",
        RequestBody.create(
          MediaType.parse("application/pdf"),
          new File("input-file.pdf")
        )
      ).addFormDataPart(
        "instructions",
        new JSONObject().put("parts", new JSONArray().put(new JSONObject().put("file", "document")
            )
          ).put("actions", new JSONArray().put(new JSONObject().put("type", "flatten")
            )
          ).toString()
      ).build();

    final Request request = new Request.Builder().url("https://api.nutrient.io/build").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());
    }
  }
}

```

### C#

```csharp

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/build");

      var request = new RestRequest(Method.POST).AddHeader("Authorization", "Bearer your_api_key_here").AddFile("document", "input-file.pdf").AddParameter("instructions", new JsonObject
        {
          ["parts"] = new JsonArray
          {
            new JsonObject
            {
              ["file"] = "document"
            }
          },
          ["actions"] = new JsonArray
          {
            new JsonObject
            {
              ["type"] = "flatten"
            }
          }
        }.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);
    }
  }
}

```

### JavaScript

```javascript

// 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(
  "instructions",
  JSON.stringify({
    parts: [
      {
        file: "document",
      },
    ],
    actions: [
      {
        type: "flatten",
      },
    ],
  }),
);
formData.append("document", fs.createReadStream("input-file.pdf"));
(async () => {
  try {
    const response = await axios.post(
      "https://api.nutrient.io/build",
      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")));
  });
}

```

### Python

```python

import requests
import json

response = requests.request(
  'POST',
  'https://api.nutrient.io/build',
  headers = {
    'Authorization': 'Bearer your_api_key_here'
  },
  files = {
    'document': open('input-file.pdf', 'rb')
  },
  data = {
    'instructions': json.dumps({
      'parts': [
        {
          'file': 'document'
        }
      ],
      'actions': [
        {
          'type': 'flatten'
        }
      ]
    })
  },
  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

```php

<?php

$FileHandle = fopen('result.pdf', 'w+');

$curl = curl_init();

curl_setopt_array($curl, array(
  CURLOPT_URL => 'https://api.nutrient.io/build',
  CURLOPT_CUSTOMREQUEST => 'POST',
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => '',
  CURLOPT_POSTFIELDS => array(
    'instructions' => '{
      "parts": [
        {
          "file": "document"
        }
      ],
      "actions": [
        {
          "type": "flatten"
        }
      ]
    }',
    'document' => new CURLFILE('input-file.pdf')
  ),
  CURLOPT_HTTPHEADER => array(
    'Authorization: Bearer your_api_key_here'
  ),
  CURLOPT_FILE => $FileHandle,
));

$response = curl_exec($curl);

curl_close($curl);

fclose($FileHandle);

```

### HTTP

```http

POST https://api.nutrient.io/build HTTP/1.1
Content-Type: multipart/form-data; boundary=--customboundary
Authorization: Bearer your_api_key_here

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

{
  "parts": [
    {
      "file": "document"
    }
  ],
  "actions": [
    {
      "type": "flatten"
    }
  ]
}
--customboundary
Content-Disposition: form-data; name="document"; filename="input-file.pdf"
Content-Type: application/pdf

(document data)
--customboundary--

```

## Simple request

The `/build` API supports inputs provided from remote URLs. If all inputs are provided as remote URLs, the multipart request isn't necessary and can be simplified to a non-multipart request with the `application/json` content type:

### Shell

```shell

curl -X POST https://api.nutrient.io/build \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer your_api_key_here" \
  -o result.pdf \
  --fail \
  -d 'null'

```

### Shell (Windows)

```powershell

curl -X POST https://api.nutrient.io/build ^
  -H "Content-Type: application/json" ^
  -H "Authorization: Bearer your_api_key_here" ^
  -o result.pdf ^
  --fail ^
  -d "null"

```

### Java

```java

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 MediaType mediaType = MediaType.parse("application/json");
    final RequestBody body = RequestBody.create(
      mediaType,
      ).toString()
    );

    final Request request = new Request.Builder().url("https://api.nutrient.io/build").method("POST", body).addHeader("Content-Type", "application/json").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());
    }
  }
}

```

### C#

```csharp

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/build");

      var request = new RestRequest(Method.POST).AddHeader("Authorization", "Bearer your_api_key_here").AddJsonBody();

      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);
    }
  }
}

```

### JavaScript

```javascript

// 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 body = JSON.stringify(null);

(async () => {
  try {
    const response = await axios.post("https://api.nutrient.io/build", body, {
      headers: {
        "Content-Type": "application/json",
        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")));
  });
}

```

### Python

```python

import requests
import json

body = json.dumps(null
)

response = requests.request(
  'POST',
  'https://api.nutrient.io/build',
  headers = {
    'Content-Type': 'application/json',
    'Authorization': 'Bearer your_api_key_here'
  },
  data = body,
  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

```php

<?php

$FileHandle = fopen('result.pdf', 'w+');

$curl = curl_init();

$body = 'null
';

curl_setopt_array($curl, array(
  CURLOPT_URL => 'https://api.nutrient.io/build',
  CURLOPT_CUSTOMREQUEST => 'POST',
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => '',
  CURLOPT_POSTFIELDS => $body,
  CURLOPT_HTTPHEADER => array(
    'Content-Type: application/json',
    'Authorization: Bearer your_api_key_here'
  ),
  CURLOPT_FILE => $FileHandle,
));

$response = curl_exec($curl);

curl_close($curl);

fclose($FileHandle);

```

### HTTP

```http

POST https://api.nutrient.io/build HTTP/1.1
Content-Type: application/json
Authorization: Bearer your_api_key_here

null

```

For more details on the structure of an API request, refer to the [API reference](https://www.nutrient.io/api/reference/public/).
---

## Related pages

- [Combine API actions in a single request](/guides/dws-processor/developer-guides/combine-workflows.md)
- [Authentication your requests](/guides/dws-processor/developer-guides/authentication.md)
- [Troubleshooting errors](/guides/dws-processor/developer-guides/errors.md)
- [Deployment options](/guides/dws-processor/developer-guides/deployment-options.md)
- [PDF generation](/guides/dws-processor/developer-guides/pdf-generation.md)
- [Performance](/guides/dws-processor/developer-guides/performance.md)
- [Web SDK integration](/guides/dws-processor/developer-guides/web-sdk-client.md)