How to watermark a PDF using Python

This post covers watermarking PDFs using our PDF watermark Python API. The free plan includes 200 credits. Different operations consume different amounts of credits, affecting the total number of documents you can process. Create a free account(opens in a new tab) to get your API key.

This guide targets Python developers working with document-heavy workflows who need programmatic PDF watermarking.

Nutrient DWS Processor API

Watermarking PDFs is one of 30+ operations available through our PDF API tools. 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

Your account provides access to all PDF API tools.

Getting started

Requirements:

• A free account for API key access
• Python installed on your system (download Python here(opens in a new tab))

Step 1 — Creating a free account on Nutrient

Visit 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 processing credits and access to all PDF API tools.

Step 2 — Obtaining the API key

After email verification, access 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). Inside watermark_pdf, create two subfolders: input_documents and processed_documents.

In the root folder (watermark_pdf), create a file called processor.py for your code.

Place your watermark image and PDF in the input_documents folder. Name them logo.png and document.pdf.

Your folder structure:

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

Step 4 — Writing the code

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

import requests
import json

response = requests.request(
  'POST',
  'https://api.nutrient.io/build',
  headers = {
    'Authorization': 'Bearer YOUR_API_KEY_HERE'
  },
  files = {
    'document': open('input_documents/document.pdf', 'rb'),
    'logo': open('input_documents/logo.png', 'rb')
  },
  data = {
    'instructions': json.dumps({
      'parts': [
        {
          'file': 'document'
        }
      ],
      'actions': [
        {
          'type': 'watermark',
          'image': 'logo',
          'width': '25%'
        }
      ]
    })
  },
  stream = True
)

if response.ok:
  with open('processed_documents/result.pdf', 'wb') as fd:
    for chunk in response.iter_content(chunk_size=8096):
      fd.write(chunk)
else:
  print(response.text)
  exit()

Code explanation

The code imports requests and json dependencies, and then creates instructions for the API call.

The requests module makes the API call. On success, the result saves to the processed_documents folder.

The instructions set the watermark width to 25 percent of the page. Adjust this value as needed.

Output

Execute the code:

python3 processor.py

After execution, a new file, result.pdf, appears in the processed_documents folder.

Final folder structure:

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

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
• Python client — Official Python library

Conclusion

This post demonstrated watermarking PDF documents in Python 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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