How to watermark a PDF using PHP

This tutorial covers watermarking PDFs using our watermark PDF PHP 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) to create your free account.

After account creation, the dashboard displays your plan details.

You start with 200 credits and access to all PDF API tools.

Step 2 — Obtaining the API key

After email verification, get your API key from the dashboard. Click API keys in the left menu to view your keys.

Copy the Live API key for use with the watermark PDF API.

Step 3 — Setting up folders and files

Create a folder called watermark_pdf and open it in a code editor. This tutorial uses VS Code. Create two subfolders: input_documents and processed_documents.

Copy your PDF file to input_documents and rename it to document.pdf. Add your watermark image to the same folder as logo.png.

In the root watermark_pdf folder, create processor.php for your code.

Your folder structure:

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

Step 4 — Writing the code

Open the processor.php file and paste the code below into it:

<?php

$FileHandle = fopen('processed_documents/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": "watermark",
          "image": "logo",
          "width": "25%"
        }
      ]
    }',
    'document' => new CURLFILE('input_documents/document.pdf'),
    'logo' => new CURLFILE('input_documents/logo.png')
  ),
  CURLOPT_HTTPHEADER => array(
    'Authorization: Bearer YOUR_API_KEY' // Replace YOUR_API_KEY_HERE with your API key.
  ),
  CURLOPT_FILE => $FileHandle,
));

$response = curl_exec($curl);

curl_close($curl);

fclose($FileHandle);

Code explanation

The FileHandle variable saves the output file to the processed_documents folder.

The instructions variable contains API instructions as a JSON string. The code then makes a CURL request to the API.

Output

Execute the code with:

php processor.php

After successful 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.php

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

Conclusion

This tutorial demonstrated how to watermark PDF documents in PHP using our watermark PDF API.

You can integrate this functionality into existing applications to add watermarks to PDF pages. The same API token provides access to 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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