curl --request POST \
  --url https://api.iyzpdf.com/v1/pdf/merge \
  --header "X-API-Key: $IYZPDF_API_KEY" \
  --form "files=@cover.pdf" \
  --form "files=@appendix.pdf" \
  --form 'order=[0,1]' \
  --output merged.pdf

import os
import requests

api_key = os.environ["IYZPDF_API_KEY"]

with open("cover.pdf", "rb") as cover_file, open("appendix.pdf", "rb") as appendix_file:
    response = requests.post(
        "https://api.iyzpdf.com/v1/pdf/merge",
        headers={"X-API-Key": api_key},
        files=[
            ("files", ("cover.pdf", cover_file, "application/pdf")),
            ("files", ("appendix.pdf", appendix_file, "application/pdf")),
        ],
        data={"order": "[0,1]"},
        timeout=60,
    )

if not response.ok:
    raise Exception(response.text)

with open("merged.pdf", "wb") as output_file:
    output_file.write(response.content)

import { readFileSync } from "node:fs";
import { writeFile } from "node:fs/promises";

const apiKey = process.env.IYZPDF_API_KEY;
const form = new FormData();

form.append("files", new Blob([readFileSync("cover.pdf")], { type: "application/pdf" }), "cover.pdf");
form.append("files", new Blob([readFileSync("appendix.pdf")], { type: "application/pdf" }), "appendix.pdf");
form.append("order", JSON.stringify([0, 1]));

const response = await fetch("https://api.iyzpdf.com/v1/pdf/merge", {
  method: "POST",
  headers: {
    "X-API-Key": apiKey
  },
  body: form
});

if (!response.ok) {
  throw new Error(await response.text());
}

await writeFile("merged.pdf", Buffer.from(await response.arrayBuffer()));

<?php

$apiKey = getenv('IYZPDF_API_KEY');

$ch = curl_init('https://api.iyzpdf.com/v1/pdf/merge');

curl_setopt_array($ch, [
    CURLOPT_POST => true,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER => [
        'X-API-Key: ' . $apiKey,
    ],
    CURLOPT_POSTFIELDS => [
        'files[0]' => new CURLFile('cover.pdf', 'application/pdf', 'cover.pdf'),
        'files[1]' => new CURLFile('appendix.pdf', 'application/pdf', 'appendix.pdf'),
        'order' => json_encode([0, 1]),
    ],
]);

$pdf = curl_exec($ch);
$status = curl_getinfo($ch, CURLINFO_HTTP_CODE);

if ($pdf === false || $status !== 200) {
    throw new RuntimeException('Request failed: ' . curl_error($ch) . PHP_EOL . $pdf);
}

file_put_contents('merged.pdf', $pdf);
curl_close($ch);

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import okhttp3.MediaType;
import okhttp3.MultipartBody;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;

public class MergePdfExample {
    public static void main(String[] args) throws IOException {
        String apiKey = System.getenv("IYZPDF_API_KEY");
        OkHttpClient client = new OkHttpClient();

        RequestBody formBody = new MultipartBody.Builder()
            .setType(MultipartBody.FORM)
            .addFormDataPart(
                "files",
                "cover.pdf",
                RequestBody.create(Files.readAllBytes(Path.of("cover.pdf")), MediaType.parse("application/pdf")))
            .addFormDataPart(
                "files",
                "appendix.pdf",
                RequestBody.create(Files.readAllBytes(Path.of("appendix.pdf")), MediaType.parse("application/pdf")))
            .addFormDataPart("order", "[0,1]")
            .build();

        Request request = new Request.Builder()
            .url("https://api.iyzpdf.com/v1/pdf/merge")
            .addHeader("X-API-Key", apiKey)
            .post(formBody)
            .build();

        try (Response response = client.newCall(request).execute()) {
            if (!response.isSuccessful() || response.body() == null) {
                String errorBody = response.body() != null ? response.body().string() : "";
                throw new IOException("Request failed: " + response.code() + " " + errorBody);
            }

            Files.write(Path.of("merged.pdf"), response.body().bytes());
        }
    }
}

var apiKey = Environment.GetEnvironmentVariable("IYZPDF_API_KEY");
using var client = new HttpClient();
using var form = new MultipartFormDataContent();
await using var first = File.OpenRead("cover.pdf");
await using var second = File.OpenRead("appendix.pdf");

client.DefaultRequestHeaders.Add("X-API-Key", apiKey);

form.Add(new StreamContent(first), "files", "cover.pdf");
form.Add(new StreamContent(second), "files", "appendix.pdf");
form.Add(new StringContent("[0,1]"), "order");

using var response = await client.PostAsync(
    "https://api.iyzpdf.com/v1/pdf/merge",
    form);

response.EnsureSuccessStatusCode();

await using var output = File.Create("merged.pdf");
await response.Content.CopyToAsync(output);

{
  "fileName": "output.pdf",
  "size": 183240,
  "creditsUsed": 1,
  "creditsRemaining": 49,
  "contentType": "application/pdf"
}

{
  "error": {
    "code": "INVALID_REQUEST",
    "message": "The request payload is invalid or incomplete."
  }
}

{
  "error": {
    "code": "UNAUTHORIZED",
    "message": "Missing or invalid API key."
  }
}

{
  "error": {
    "code": "INSUFFICIENT_CREDITS",
    "message": "You need more credits to complete this request.",
    "creditsRequired": 2,
    "creditsBalance": 0,
    "purchaseUrl": "https://iyzpdf.com/portal/credits"
  }
}

{
  "error": {
    "code": "FILE_TOO_LARGE",
    "message": "The uploaded file or request body exceeds the allowed size limit."
  }
}

{
  "error": {
    "code": "UNSUPPORTED_MEDIA_TYPE",
    "message": "The uploaded file type or content type is not supported."
  }
}

{
  "error": {
    "code": "RATE_LIMIT_EXCEEDED",
    "message": "Too many requests. Please retry after the rate limit resets."
  }
}

{
  "error": {
    "code": "PROCESSING_FAILED",
    "message": "The document could not be processed."
  }
}