How to watermark a PDF using JavaScript

This post covers watermarking PDFs using our watermark PDF JavaScript API. The free plan includes 200 credits. Different operations consume different amounts of credits, so document processing limits vary. Create a free account(opens in a new tab) to get your API key.

Nutrient DWS Processor API

Watermarking PDFs is one of 30+ operations available through our PDF API tools. You can combine watermarking with other tools to build document processing workflows:

• Convert MS Office files and images to PDF, and then add watermarks
• Duplicate or delete PDF pages before watermarking
• Merge or flatten PDFs, and then watermark the result

After creating your account, you can access all PDF API tools.

Step 1 — Creating a free account on Nutrient

Go to our website(opens in a new tab), where you’ll see the page below, prompting you to create your free account.

Once you’ve created your account, you’ll be welcomed by a page showing an overview of your plan details.

You’ll start with 200 credits to process, and you’ll be able to access all our PDF API tools.

Step 2 — Obtaining the API key

After you’ve verified your email, you can get your API key from the dashboard. In the menu on the left, click API keys. You’ll see the following page, which is an overview of your keys.

Copy the Live API key, because you’ll need this for the watermark PDF API.

Step 3 — Setting up folders and files

First, create a folder called watermark_pdf and open it in a code editor. For this tutorial, you’ll use VS Code as your primary code editor. Next, create two folders inside watermark_pdf and name them input_documents and processed_documents.

Now, copy your PDF file to the input_documents folder and rename it to document.pdf. Then, place an image that you want to use to watermark the PDF pages in this folder and name it logo.png.

Finally, in the root folder, watermark_pdf, create a file called processor.js. This is the file where you’ll keep your code.

Your folder structure will look like this:

watermark_pdf
├── input_documents
|    └── document.pdf
|    └── logo.png
├── processed_documents
└── processor.js

Step 4 — Installing dependencies

To get started watermarking PDFs, you first need to install the following dependencies:

• axios(opens in a new tab) — This package is used for making REST API calls.
• Form-Data(opens in a new tab) — This package is used for creating form data.

Use the commands below to install both of them:

npm install form-data
npm install axios

Step 5 — Writing the code

Now, open the processor.js file and paste the code below into it:

// 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: "watermark",
      image: "logo",
      width: "25%"
    }
  ]
}))
formData.append('document', fs.createReadStream('input_documents/document.pdf'))
formData.append('logo', fs.createReadStream('input_documents/logo.png'))

(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("processed_documents/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")))
  })
}

Code explanation

The code creates a formData variable with API instructions. The createReadStream method reads input files from the input_documents folder. The axios.post function makes the API call, and the response streams directly to result.pdf in the processed_documents folder.

Output

Execute the code:

node processor.js

After execution, result.pdf appears in the processed_documents folder.

Final folder structure:

watermark_pdf
├── input_documents
|    └── document.pdf
|    └── logo.png
├── processed_documents
|    └── result.pdf
└── processor.js

Additional resources

Explore more ways to work with Nutrient API:

• Postman collection — Test API endpoints directly in Postman
• Zapier integration — Automate document workflows without code
• MCP Server — PDF automation for LLM applications
• JavaScript SDK — Official JavaScript library

Conclusion

This post demonstrated watermarking PDF documents in JavaScript using our watermark PDF API.

Integrate this functionality into existing applications to watermark PDF pages. The same API token enables other operations: merging documents, running OCR, duplicating pages, and more. Sign up(opens in a new tab) for a free trial.

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