> ## Documentation Index
> Fetch the complete documentation index at: https://developers.gonitro.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Merge PDFs

> Combine several PDFs into one inside a Zap with the Nitro PDF Services app.

Combines up to 25 PDFs into a single document, in the order they are provided.

## Inputs

| Field | Required | Description |
| - | - | - |
| **PDF Files** | Yes | A list of PDFs. **Order matters** — files are merged in the order you add them. Up to 25. |
| **Output Type** | Yes | *Download file* (default) or *Download URL*. |

Because **PDF Files** is a list field, you can map a line-item group from an earlier step into it,
or add entries one at a time in the Zap editor. The step fails with an `InvalidInput` error before
calling Nitro if the list is empty or has more than 25 files.

## Outputs

<Tabs>
  <Tab title="Download file">
    | Field | Description |
    | - | - |
    | **Merged PDF File** | The combined PDF |
  </Tab>

  <Tab title="Download URL">
    | Field | Description |
    | - | - |
    | **Merged PDF URL** | Download URL, valid for about 15 minutes |
    | **Content Type** | `application/pdf` |
    | **File Size Bytes** | Size of the merged file |
    | **Page Count** | Total pages across all inputs |
  </Tab>
</Tabs>

## Example Zap

Attach a standard cover sheet to every report as it is generated.

<Steps>
  <Step title="Google Drive — New File in Folder">
    Watch the folder reports land in.
  </Step>

  <Step title="Google Drive — Find a File">
    Look up the fixed `cover.pdf` in your templates folder.
  </Step>

  <Step title="Nitro PDF Services — Merge PDFs">
    * **PDF Files** → first the cover sheet from step 2, then the report from step 1.
    * **Output Type** → *Download file*.
  </Step>

  <Step title="Gmail — Send Email">
    Attach **Merged PDF File**.
  </Step>
</Steps>

<Tip>
  To merge a variable number of files, collect them with a **Looping by Zapier** step and a line-item
  group, then map the group into **PDF Files** in a single Merge step — one Nitro call rather than
  one per file. For more than 25 files, merge in batches and then merge the batches.
</Tip>

## Related

* [Actions](/docs/integrations/zapier/actions)
* [Working with files](/docs/integrations/zapier/working-with-files)