Automate PDF Watermarking: Add Logos to Documents in Bulk

require 'rest-client'
require 'json'

response = RestClient.post(
  'https://apdf.io/api/pdf/page/overlay',
  {
    file: 'https://your-server.com/contract.pdf',
    overlay: 'https://your-server.com/confidential-watermark.pdf',
    repeat: '1'
  },
  {
    Authorization: 'Bearer YOUR_API_TOKEN',
    Accept: 'application/json',
    content_type: 'application/json'
  }
)

result = JSON.parse(response.body)
puts result['file']  # URL to the watermarked PDF

That is it. Your contract now has the watermark applied to every page.

The "overlay" operation takes two PDFs and layers one on top of the other:

• file - Your original document (the contract)
• overlay - The watermark PDF (semi-transparent "CONFIDENTIAL" text or your logo)
• repeat - Repeat the "overlay" operation with page 1 from the watermark PDF on all pages

The API merges them, placing the overlay on top of each page. If your watermark has transparency, the original content shows through perfectly.

Your watermark needs to be a PDF file. Here are two common approaches:

Option A: Use a Design Tool
Create a single-page PDF in Canva, Figma, or Adobe Illustrator. Add your "CONFIDENTIAL" text or logo with 20-30% opacity. Export as PDF.

Option B: Use HTML
You can use the aPDF.io Create endpoint to generate a watermark PDF from HTML. This gives you full control over positioning and transparency.

<div style="
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%) rotate(-45deg);
  font-size: 80px;
  color: rgba(255, 0, 0, 0.15);
  font-weight: bold;
">
  CONFIDENTIAL
</div>

1. Sign up at aPDF.io (it's free).
2. Copy your API Token from the dashboard.

Here is a complete Ruby script that processes multiple contracts and adds a watermark to each one:

require 'rest-client'
require 'json'

API_TOKEN = 'YOUR_API_TOKEN_HERE'
API_URL = 'https://apdf.io/api/pdf/page/overlay'

# The watermark PDF (semi-transparent "CONFIDENTIAL" stamp)
WATERMARK_URL = 'https://your-server.com/confidential-watermark.pdf'

# List of contracts to watermark
contracts = [
  'https://your-server.com/contracts/contract-001.pdf',
  'https://your-server.com/contracts/contract-002.pdf',
  'https://your-server.com/contracts/contract-003.pdf'
]

puts "Starting bulk watermarking...\n"

contracts.each_with_index do |contract_url, index|
  begin
    puts "Processing contract #{index + 1}/#{contracts.length}..."

    response = RestClient.post(
      API_URL,
      {
        file: contract_url,
        overlay: WATERMARK_URL,
        repeat: '1'
      },
      {
        Authorization: "Bearer #{API_TOKEN}",
        Accept: 'application/json',
        content_type: 'application/json'
      }
    )

    result = JSON.parse(response.body)

    puts "  Done: #{result['file']}"

  rescue RestClient::ExceptionWithResponse => e
    puts "  Error: #{e.response}"
  rescue => e
    puts "  Error: #{e.message}"
  end
end

puts "\nBulk watermarking complete!"

Starting bulk watermarking...
Processing contract 1/3...
  Done: https://apdf-files.s3.eu-central-1.amazonaws.com/a1b2c3d4.pdf
Processing contract 2/3...
  Done: https://apdf-files.s3.eu-central-1.amazonaws.com/e5f6g7h8.pdf
Processing contract 3/3...
  Done: https://apdf-files.s3.eu-central-1.amazonaws.com/i9j0k1l2.pdf

Bulk watermarking complete!

Each URL is a watermarked version of the original contract. You can download them or send them directly to recipients. Note: These URLs are valid for 1 hour.

Sometimes you only want the watermark on specific pages. The API provides two parameters for this:

• from - Which pages from the watermark PDF to use
• to - Which pages in your document should receive the watermark

For example, to watermark only pages 2 through 5 of your contract:

response = RestClient.post(
  API_URL,
  {
    file: contract_url,
    overlay: WATERMARK_URL,
    to: '2-5',  # Only watermark pages 2, 3, 4, and 5
    repeat: '1'
  },
  {
    Authorization: "Bearer #{API_TOKEN}",
    Accept: 'application/json',
    content_type: 'application/json'
  }
)

Use to: '2-z' to watermark from page 2 to the end (useful for skipping cover pages).

The same technique works for adding company logos to documents. Create a PDF with your logo positioned in the corner (with transparency), then overlay it onto your documents.

This is commonly used for:

• Branding white-label reports with your company logo
• Adding "DRAFT" stamps to preliminary documents
• Stamping "APPROVED" or "REVIEWED" on processed files
• Adding page numbers or headers to existing PDFs

Watermarking PDFs manually is tedious. With the aPDF.io Overlay API, you can process hundreds of documents in seconds. The watermark stays consistent, and your Ruby script can be scheduled to run automatically whenever new documents arrive.

• Protect the Documents: Use the Password Protection endpoint to prevent recipients from editing the watermarked files.
• Merge Multiple Documents: Combine watermarked contracts with cover letters using the Merge endpoint.