Merge PDFs

Merge PDFs is an API that combines several PDFs into one, in the order you send them. Great for joining invoices, attachments or reports into a single file from n8n, Make or Zapier, with no servers to maintain.

How it works

You send two or more PDFs (base64-encoded, inside a JSON body) and get back a single PDF with every page from all of them, in the same order you sent them. Nothing is stored: the PDF is generated on the fly.

Unlike the other PDF tools, this one needs several files at once, so it only accepts a JSON body (there's no "paste the raw PDF" mode).

All you need

Your API key. Create it in your dashboard with "+ Create key". It's shown only once, so copy and save it.
In your automation platform, an "HTTP Request" step (n8n, Make, Zapier, Pipedream… all have one).
Each PDF converted to base64 before sending it (see the step-by-step below).

The PDFs travel inside a JSON body, so all the files you merge together can't add up to more than about 4 MB combined. For bigger PDFs, shrink them first or merge in batches.

How to use it in n8n (step by step)

In the HTTP Request node:

Method: POST
URL: https://api.cofferdock.com/pdf-merge
Send Headers: on → add two: x-api-key = your key, and Content-Type = application/json
Send Body: on → Body Content Type: JSON → { "files": ["<first PDF base64>", "<second PDF base64>"], "output": "binary" }
Under Options → Response → Response Format: choose File (since you asked for output: "binary")

If the PDF arrives as binary data from an earlier step (say, from Google Drive or an email), convert it to base64 with a Code node using {{'{{'}}$binary.data.toString('base64'){{'}}'}}, or with the Move Binary Data node in "Binary to Property" mode.

In Make (HTTP → Make a request module): same method and URL, Headers with the two headers, Body type: Raw, Content type: JSON (application/json), and the same JSON with the files array in Request content. Make's "Get a file" module already gives you base64 content directly.

In short: POST to …/pdf-merge, headers x-api-key and Content-Type: application/json, a JSON body with files (array of base64 PDFs) and output: "binary", Response Format as File.

Options (inside the JSON)

Option	Default	What it does
`files`	-	Required. Array of 2 to 20 base64 PDFs, in the order you want them merged.
`output`	`json`	Set to `binary` to receive the PDF directly instead of base64.

API overview

Endpoint: POST https://api.cofferdock.com/pdf-merge
Auth: header x-api-key: YOUR_KEY.
Input: application/json ONLY: { "files": ["<base64>", ...] }, 2 to 20 files. There's no raw mode (more than one file doesn't fit in it).
Output: JSON with the base64 PDF by default; with "output": "binary" it returns the binary (application/pdf) directly.
Limits: the full JSON body (all base64 files together) is capped at 6 MB, meaning about 4 MB of real combined PDF across all files. 30 requests/min per IP. 1 merge = 1 credit, no matter how many files you combine.

Options

Option	Default	Description
`files`	-	Required. Array of 2 to 20 base64 strings.
`output`	`json`	`json` (base64) or `binary` (raw PDF).

Examples

curl (base64-encode two PDFs and merge them):

B64_1=$(base64 -w0 file1.pdf)
B64_2=$(base64 -w0 file2.pdf)
curl -X POST "https://api.cofferdock.com/pdf-merge" \
  -H "x-api-key: YOUR_KEY" \
  -H "Content-Type: application/json" \
  -d "{\"files\":[\"$B64_1\",\"$B64_2\"],\"output\":\"binary\"}" \
  -o merged.pdf

JavaScript (Node 18+):

const fs = require('fs');
const files = ['file1.pdf', 'file2.pdf'].map((f) => fs.readFileSync(f).toString('base64'));
const r = await fetch('https://api.cofferdock.com/pdf-merge', {
  method: 'POST',
  headers: { 'x-api-key': 'YOUR_KEY', 'Content-Type': 'application/json' },
  body: JSON.stringify({ files, output: 'binary' }),
});
const buffer = Buffer.from(await r.arrayBuffer());
fs.writeFileSync('merged.pdf', buffer);

Python:

import base64, requests
files = [base64.b64encode(open(f, 'rb').read()).decode() for f in ['file1.pdf', 'file2.pdf']]
r = requests.post(
    'https://api.cofferdock.com/pdf-merge',
    headers={'x-api-key': 'YOUR_KEY', 'Content-Type': 'application/json'},
    json={'files': files, 'output': 'binary'},
)
open('merged.pdf', 'wb').write(r.content)

Default response (JSON with base64)

Without output, the response carries the merged PDF in base64:

{ "files": ["JVBERi0xLjQ…", "JVBERi0xLjQ…"] }
→ { "success": true, "pdf": "JVBERi0xLjQ…", "mime_type": "application/pdf",
    "meta": { "files_merged": 2, "total_pages": 7, "used": 12, "remaining": 488 } }

What you get back

By default, a JSON object with the merged PDF in base64 plus data like the total page count. With "output": "binary" you get the PDF itself, ready to save or send.