← PDF merger

Merge PDF files in Node.js

Combine up to 20 PDFs into one, in the order you send them. Pages are copied as they are, with no loss of quality. Here is the whole call in Node.js, with the output it produced when we ran it.

Before you start

• An API key. Create a free account; it comes with free tokens every month. Put the key in an environment variable so it stays out of your code: export BLOODWEB_KEY=your_key
• Node.js 18 or later. Nothing to install: fetch, FormData and Blob are built in. Save the file with the .mjs ending so await works at the top level.
• The input files in the same folder: part1.pdf, part2.pdf. Use your own; those are the names the code expects.

The code

Save it as pdf-merge.mjs and run node pdf-merge.mjs.

// Node.js 18 or later: fetch, FormData and Blob are built in.
import { readFile, writeFile } from "node:fs/promises";

const form = new FormData();
form.append("files[]", new Blob([await readFile("part1.pdf")]), "part1.pdf");
form.append("files[]", new Blob([await readFile("part2.pdf")]), "part2.pdf");

const res = await fetch("https://bloodweb.net/api/v1/pdf-merge", {
  method: "POST",
  headers: { Authorization: `Bearer ${process.env.BLOODWEB_KEY}` },
  body: form,
});
if (!res.ok) throw new Error(`${res.status}: ${(await res.json()).error.message}`);
await writeFile("merged.pdf", Buffer.from(await res.arrayBuffer()));

What you get

Tested 19 October 2026: this exact code ran against our test copy of the API, which runs the same service code as bloodweb.net, and produced this.

It writes merged.pdf: a PDF, 4 pages, 2 KB.

If it fails

A failed call is not charged. The answer is JSON with an error object; the code above prints its message. The usual ones:

• 401 missing_key or invalid_key: BLOODWEB_KEY is not set in the shell that runs the code, or the key was revoked.
• 415 unsupported_type: the file is not a type this service reads. The type is read from the file itself, so renaming a file does not change it.
• 413 file_too_large: the file is over the limit on the service page.
• 402 insufficient_tokens: the balance does not cover the call. Top up in the dashboard.
• 429 rate_limited: too many calls at once. Wait the seconds in the Retry-After header and send it again.

Every code and its fix is in the docs.

Next

• The PDF merger page: every option, the limits, and Try it now in your browser.
• Getting started: keys, errors and rate limits for all the services.