---
name: "pdf123-overlay-pdfs"
description: "Overlay one PDF on top of another. Runs the PDF123 \"Overlay PDFs\" 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: 叠加 PDF, Superponer PDF, PDF चढ़ाएँ, تراكب PDF, Sobrepor PDFs, Tumpangkan PDF, Superposer des PDF, Наложить PDF, PDFの重ね合わせ, PDFs überlagern, PDF 겹치기, Chồng PDF, PDF bindir, 疊加 PDF, Sovrapponi PDF, ซ้อน PDF, Nałóż PDF, Накласти PDF, PDF's over elkaar leggen, Tindih PDF, Lägg PDF över PDF, Επικάλυψη PDF, Наслагване на PDF, Superposa PDF, Pangisha PDF."
compatibility: "Needs curl 7.76+ and outbound HTTPS to pdf123.xyz, or PDFX_API_BASE pointing at a self-hosted pdfx-server."
---

# Overlay PDFs (PDF123)

Overlay one PDF on top of another.

Web version: https://pdf123.xyz/overlay-pdfs · All tools: https://pdf123.xyz/skills/pdf123.md

## When to use

- Stamp a letterhead PDF onto every page of a letter
- Put a draft overlay in the background
- Repeat a one-page confidential mark across a long 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/overlay-pdfs" \
  -F "fileInput=@input.pdf" \
  -F "overlayFiles=@overlayFiles.pdf" \
  -F "overlayMode=SequentialOverlay" \
  -F "overlayPosition=0" \
  --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 (one file) |
| `overlayFiles` | file | yes | | Overlay PDF(s): .pdf (repeat for several) |
| `overlayMode` | choice | yes | `SequentialOverlay` | Overlay mode. One of: `SequentialOverlay` (Sequential), `InterleavedOverlay` (Interleaved (round-robin)), `FixedRepeatOverlay` (Fixed repeat) |
| `overlayPosition` | choice | yes | `0` | Overlay layer. One of: `0` (Foreground), `1` (Background) |

## 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

- overlayMode is a dead field
- The output is rebuilt page by page: links, form fields, bookmarks and metadata of the base PDF are not kept, and page rotation flags are dropped
- Not Merge and not image-only (use Add Image)
- Password-protected files need the password; API callers run Unlock first
- 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`.