---
name: "pdf123-merge"
description: "Combine multiple PDFs into one document. Runs the PDF123 \"Merge\" tool (pdf123.xyz) over its REST API with curl, no account needed. Use when the user wants this done to their file. Also known as: 合并 PDF, Unir PDF, PDF मिलाएँ, دمج PDF, Juntar PDF, Gabungkan PDF, Fusionner des PDF, Объединить PDF, PDFの結合, PDF zusammenführen, PDF 병합, Gộp PDF, PDF birleştir, 合併 PDF, Unisci PDF, รวม PDF, Połącz PDF, Об’єднати PDF, PDF's samenvoegen, Slå ihop PDF, Συγχώνευση PDF, Обединяване на PDF, Uneix PDF, Unganisha PDF."
compatibility: "Needs curl 7.76+ and outbound HTTPS to pdf123.xyz, or PDFX_API_BASE pointing at a self-hosted pdfx-server."
---

# Merge (PDF123)

Combine multiple PDFs into one document.

Web version: https://pdf123.xyz/merge · All tools: https://pdf123.xyz/skills/pdf123.md

## When to use

- Assemble a contract and its scanned exhibits into one sendable PDF
- Combine chapter exports from different tools into a single manuscript
- Bundle receipts for expense software that accepts one file

## Run it

Replace the sample file names and values with the user's, then run:

```bash
API="${PDFX_API_BASE:-https://pdf123.xyz}"
curl -sS --fail-with-body -X POST "$API/api/v1/general/merge-pdfs" \
  -F "fileInput=@first.pdf" \
  -F "fileInput=@second.pdf" \
  --output-dir "pdf123-output/$(date +%Y%m%d-%H%M%S)" --create-dirs -OJ -w '%{filename_effective} %{content_type}\n'
```

## Inputs

Everything is `multipart/form-data`. The command above already sends each field with its default; keep them all and change only the values the user asked for, since some endpoints reject a missing optional field.

| Field | Type | Required | Default | Notes |
| --- | --- | --- | --- | --- |
| `fileInput` | file | yes | | .pdf (repeat the part once per file, at least 2; order is kept) |

## Result

curl saves the result in a new `pdf123-output/<timestamp>/` directory under the server's file name and prints its path and content type. Several output files come back as one ZIP. Tell the user where the file is.

## Limits

- Password-protected files need the password; API callers run Unlock first
- Bookmarks from the source files are not carried into the merged file
- Very large batches take longer; merge in stages
- Broken xref tables may need Repair before merge
- Upload limit on this website: 500 MB per file, sent in chunks above about 95 MB. A single direct API request body is capped at 100 MB.

## Errors

- A non-zero curl exit means the request failed. The saved file then holds `application/problem+json`; read it and report its `detail` to the user instead of retrying blindly.
- `413`: the upload exceeds 100 MiB. `429`: wait for `Retry-After` seconds, then retry once.
- Send `X-API-KEY: $PDFX_API_KEY` only if the user has a PDF123 API key; anonymous calls work without it.

## Privacy

Files are uploaded to the API host, processed, and deleted once the response is sent. For confidential files, ask before uploading, or use a self-hosted server via `PDFX_API_BASE`.