How to merge PDFs using PHP

In this post, you’ll learn how to combine multiple PDF files using our merge PDF PHP API. With our API, you receive 200 credits with the free plan. Different operations on a document consume different amounts of credits, so the number of PDF documents you can generate may vary. You’ll just need to create a free account(opens in a new tab) to get access to your API key.

Nutrient DWS Processor API

Document merging is just one of our 30+ PDF API tools. You can combine our merging tool with other tools to create complex document processing workflows, such as:

• Converting MS Office files and images into PDFs before merging
• Performing OCR on several documents before merging
• Merging, watermarking, and flattening PDFs

Once you create your account, you’ll be able to access all our 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 the page below, which shows an overview of your plan details.

As you can see in the bottom-left corner, you’ll start with 200 credits to process, and you’ll be able to access all our PDF API tools.

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

Step 2 — Setting up files and folders

Now, create a folder called merge_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 merge_pdf and name them input_documents and processed_documents.

Then, in the root folder, merge_pdf, create a file called processor.php. This is the file where you’ll keep your code.

Step 3 — 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": "first_half"
        },
        {
          "file": "second_half"
        }
      ]
    }',
    'first_half' => new CURLFILE('input_documents/first_half.pdf'),
    'second_half' => new CURLFILE('input_documents/second_half.pdf')
  ),
  CURLOPT_HTTPHEADER => array(
    'Authorization: Bearer YOUR_API_KEY_HERE'
  ),
  CURLOPT_FILE => $FileHandle,
));

$response = curl_exec($curl);

curl_close($curl);

fclose($FileHandle);

Code explanation

In the code above, you created and opened the php_result.pdf file under processed_documents. Then, you created a variable called instructions that contains all the information regarding the payload.

In the next part, you made a CURL POST request to your API endpoint, and in the parameters, first_half contains the first PDF, while second_half contains the second PDF.

Step 4 — Output

To execute the code, run the command below:

php processor.php

On successful execution, you’ll see a new processed file, php_result.pdf, which is located in the processed_documents folder.

The folder structure will look like this:

merge_pdf
├── input_documents
|    └── first_half.pdf
|    └── second_half.pdf
├── processed_documents
|    └── php_result.pdf

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

In this post, you learned how to merge files for your PHP application into a single PDF using our merge PDF API.

If you have a more complex use case, you can use our other tools to add watermarks, perform OCR, and edit (split, flatten, delete, duplicate) documents — and you can even combine these tools. To get started with a free trial, sign up here(opens in a new tab).

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