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POST
/
transformations
Merge PDF
curl --request POST \
  --url https://api.gonitro.dev/transformations \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: multipart/form-data' \
  --form method=merge \
  --form 'files[0]=@SampleFile1.pdf' \
  --form 'files[1]=@SampleFile2.pdf' \
  --form files.items.0='@example-file'
{
  "file": {
    "URL": "<string>",
    "contentType": "application/json",
    "metadata": {
      "fileSizeBytes": 123,
      "pageCount": 123
    }
  }
}
The Merge method of the Transformations endpoint combines multiple PDF files into a single PDF, placing the pages of each file in order. For example, merging: File 1 (2 pages) File 2 (3 pages) produces one PDF with 5 pages in this sequence: File 1 page 1 → File 1 page 2 → File 2 page 1 → File 2 page 2 → File 2 page 3. The method only requires the list of input files and returns a single merged PDF. No additional parameters are needed.

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Output File Format

The endpoint can return output either as JSON or as a binary file. The format depends on the Accept header (details below), which defaults to application/json.

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Processing

When requesting JSON, you can run the operation synchronously or asynchronously. This is determined by the Prefer header (details below).
  • In sync mode, the response includes a URL pointing to the processed file.
  • In async mode, the request creates a Job, and the response contains the Job ID and status so you can track progress.
Binary (octet-stream) responses are only available for synchronous operations.

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Custom File Delivery

The endpoint supports custom file-delivery destinations through the optional delivery parameter. You can provide an upload target, such as your own PUT endpoint or a pre-signed S3 URL, and Nitro will upload the resulting file there. This works for both synchronous and asynchronous processing.

  • ​
    Sync delivery

    In synchronous calls, the delivery parameter lets you direct Nitro to upload the output file to a custom URL endpoint or a pre-signed URL (e.g S3), by providing an upload url in the uploadResultTo or uploadResultsTo properties.

    ​
    Custom endpoint

    If implementing the upload endpoint by yourself, make sure your code or middleware configuration accepts requests without content-type headers.

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    S3 delivery

    If you are using S3 to manage delivery uploads, follow this AWS documentation to generate a pre-signed PUT URL.
    If using the AWS provided Python script, omit the Content-Type in Params to get the pre-signed url. For example:
     
        url = generate_presigned_url(
        s3_client,
        "put_object",
        { 
            "Bucket": args.bucket, 
            "Key": args.key,
            # Content-Type: "application/octet-stream" => Omit!
        },
    1000)

  • ​
    Async delivery

    In asynchronous flows, you can also provide a custom URL or pre-signed S3 object via uploadResultTo or uploadResultsTo, to upload your file(s) once the Job is done processing.

    ​
    Callback

    For asynchronous processing, you can also include a callback URL within the delivery parameter. This callback is a POST endpoint that Nitro will call once the Job is created and running, providing details about the file-processing job. Example of Nitro’s callback request body: 
    {
    "jobID": "babe2aa7-9b5d-4eb2-a679-5fc12cf0a490",
    "location": "https://api.gonitro.dev/jobs/babe2aa7-9b5d-4eb2-a679-5fc12cf0a490"
}

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Response behavior Matrix

This matrix shows the expected response behavior based on content type, sync/async mode, and custom file-delivery settings.
JSON (application/json)Binary (application/octet-stream)
SynchronousReturns a JSON object with a file(s) URL(s).Returns the processed file directly as binary.
Asynchronous (respond-async)Returns a JSON object with a Job ID and status.Async preference ignored, returns sync binary.
Synchronous deliveryFile delivered to custom endpoint / Bucket, returns success confirmation.N/A
Asynchronous deliveryReturns a JSON object with a Job ID and status. The file(s) will be uploaded to the provided PUT endpoint / S3 Bucket at the end of process. If callback url is provided, Nitro will notify the endpoint with a JOB ID and location.N/A

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Limits

The Platform API has the following limits:
  • File size: Maximum of 25 MB per request. This applies to single-file and multi-file requests.
  • Page count: Maximum of 250 pages per individual document. This applies to single-file and multi-file requests. Multiple documents may exceed 250 pages in total.
  • Retention time: Inputs and outputs are deleted approximately 15 minutes after the operation completes.

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Request

Authorizations

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Authorization
string
header
required

Bearer authentication header of the form Bearer <token>, where <token> is your auth token.

Headers

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Accept
enum<string>
default:*/*

Controls response format and behavior. See endpoint description above for detailed response combinations.

  • application/json: Returns JSON response with operation result
  • application/octet-stream: Returns binary file content
  • */*: Defaults to JSON response
Available options:
application/json,
application/octet-stream,
*/*
​
Prefer
enum<string>

Controls synchronous vs asynchronous operation. See endpoint description above for behavior details.

  • respond-async: Makes request asynchronous, returns job status for polling
  • No value: Synchronous response
Available options:
respond-async

Body

multipart/form-data
​
method
enum<string>
default:merge
required

The Transformations' endpoint method: merge

Available options:
merge
​
files
(file | object)[]
required

The files to process. They can be provided as a binary uploads or as a JSON with remote file references.

Example:
["@SampleFile1.pdf", "@SampleFile2.pdf"]
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delivery
object

This endpoint lets you supply your own URL to receive the single-file output. The URL may point to a custom API endpoint or a pre-signed S3 URL.

The HTTP method defaults to PUT, but you can change it based on your implementation needs via the verb parameter. You can also provide custom headers, such as authentication headers or any others required by your endpoint.

Response

Returns either JSON or binary output depending on the Accept header (defaults to JSON). JSON responses include a file URL for synchronous tasks or a job status for asynchronous tasks.

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file
object