# Split a PDF by file size

Split a PDF into smaller documents, each no larger than a maximum byte size.

Split a PDF document into multiple smaller documents, each no larger than a
maximum file size in bytes. This action returns multiple documents, packaged into
a single response according to the `Accept` header. The API is stateless: your
document is processed in-region and never stored.

## Endpoint

<Endpoint method="POST" path="/v1/split_by_size" />

Available in every region. See [Regions & data residency](/docs/api/regions-and-data-residency)
for routing and data residency.

| Region         | URL                                              |
| -------------- | ------------------------------------------------ |
| Global         | `https://api.pdfblocks.com/v1/split_by_size`     |
| United States  | `https://us.api.pdfblocks.com/v1/split_by_size`  |
| US HIPAA       | `https://hipaa.api.pdfblocks.com/v1/split_by_size` |
| European Union | `https://eu.api.pdfblocks.com/v1/split_by_size`  |
| United Kingdom | `https://uk.api.pdfblocks.com/v1/split_by_size`  |
| Canada         | `https://ca.api.pdfblocks.com/v1/split_by_size`  |
| Australia      | `https://au.api.pdfblocks.com/v1/split_by_size`  |
| Japan          | `https://jp.api.pdfblocks.com/v1/split_by_size`  |
| India          | `https://in.api.pdfblocks.com/v1/split_by_size`  |
| Brazil         | `https://br.api.pdfblocks.com/v1/split_by_size`  |

## Authentication

Authenticate every request with your secret API key in the `X-API-Key` header,
over HTTPS. Create and manage keys from the
[dashboard](https://dashboard.pdfblocks.com). See
[Authentication](/docs/api/authentication) for details.

## Request

The endpoint accepts a `multipart/form-data` request body.

<ParamField name="file" type="file" required>
  The input PDF document.
</ParamField>

<ParamField name="maximum_bytes" type="integer" required>
  The maximum size, in bytes, of each output PDF. Must be `1` or greater.
</ParamField>

## Examples

Split a document so each part is at most 1 MB:

<CodeGroup>

```bash title="cURL"
curl https://api.pdfblocks.com/v1/split_by_size \
  -H 'X-API-Key: your_api_key' \
  -F file=@input.pdf \
  -F maximum_bytes=1048576 \
  -o parts.zip
```

```python title="Python"
# pip install requests
import requests

with open('input.pdf', 'rb') as file:
    response = requests.post(
        'https://api.pdfblocks.com/v1/split_by_size',
        headers={'X-API-Key': 'your_api_key'},
        files={'file': file},
        data={'maximum_bytes': 1048576},  # 1 MB
    )

response.raise_for_status()
with open('parts.zip', 'wb') as output:
    output.write(response.content)
```

```javascript title="Node.js"
// Node.js 18+
import { readFile, writeFile } from 'node:fs/promises';

const body = new FormData();
body.set('file', new Blob([await readFile('input.pdf')]), 'input.pdf');
body.set('maximum_bytes', '1048576'); // 1 MB

const response = await fetch('https://api.pdfblocks.com/v1/split_by_size', {
  method: 'POST',
  headers: { 'X-API-Key': 'your_api_key' },
  body,
});

if (!response.ok) throw new Error(`Request failed: ${response.status}`);
await writeFile('parts.zip', Buffer.from(await response.arrayBuffer()));
```

```php title="PHP"
<?php
$ch = curl_init('https://api.pdfblocks.com/v1/split_by_size');
curl_setopt_array($ch, [
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER => ['X-API-Key: your_api_key'],
    CURLOPT_POST => true,
    CURLOPT_POSTFIELDS => [
        'file' => new CURLFile('input.pdf', 'application/pdf'),
        'maximum_bytes' => '1048576', // 1 MB
    ],
]);

$zip = curl_exec($ch);
if (curl_getinfo($ch, CURLINFO_HTTP_CODE) === 200) {
    file_put_contents('parts.zip', $zip);
}
```

```ruby title="Ruby"
# gem install http
require 'http'

response = HTTP
  .headers('X-API-Key' => 'your_api_key')
  .post('https://api.pdfblocks.com/v1/split_by_size', form: {
    file: HTTP::FormData::File.new('input.pdf'),
    maximum_bytes: '1048576', # 1 MB
  })

File.write('parts.zip', response.body) if response.status.success?
```

```go title="Go"
package main

import (
	"bytes"
	"io"
	"mime/multipart"
	"net/http"
	"os"
)

func main() {
	var buf bytes.Buffer
	form := multipart.NewWriter(&buf)

	file, _ := os.Open("input.pdf")
	defer file.Close()
	part, _ := form.CreateFormFile("file", "input.pdf")
	io.Copy(part, file)

	form.WriteField("maximum_bytes", "1048576") // 1 MB
	form.Close()

	req, _ := http.NewRequest("POST", "https://api.pdfblocks.com/v1/split_by_size", &buf)
	req.Header.Set("Content-Type", form.FormDataContentType())
	req.Header.Set("X-API-Key", "your_api_key")

	res, _ := http.DefaultClient.Do(req)
	defer res.Body.Close()

	out, _ := os.Create("parts.zip")
	defer out.Close()
	io.Copy(out, res.Body)
}
```

```csharp title="C#"
using var client = new HttpClient();
client.DefaultRequestHeaders.Add("X-API-Key", "your_api_key");

using var form = new MultipartFormDataContent
{
    { new ByteArrayContent(File.ReadAllBytes("input.pdf")), "file", "input.pdf" },
    { new StringContent("1048576"), "maximum_bytes" }, // 1 MB
};

var response = await client.PostAsync(
    "https://api.pdfblocks.com/v1/split_by_size", form);
response.EnsureSuccessStatusCode();
await File.WriteAllBytesAsync(
    "parts.zip", await response.Content.ReadAsByteArrayAsync());
```

</CodeGroup>

## Response

This action returns multiple documents, packaged into a single response
according to the `Accept` request header — see
[Response formats & content negotiation](/docs/api/response-formats) for the full
negotiation reference. With no `Accept` header, the default is a ZIP archive:

```http
HTTP/1.1 200 OK
Content-Type: application/zip
```

Select the packaging with the `Accept` header:

| `Accept` header      | Response                                                        |
| -------------------- | -------------------------------------------------------------- |
| *(none sent)*        | `application/zip` — the default                                |
| `application/zip`    | A ZIP archive of the output PDFs                               |
| `application/json`   | A JSON envelope of base64-encoded documents                    |
| `multipart/mixed`    | One PDF per part                                               |
| anything else        | `406 Not Acceptable`                                            |

The output documents are named `00001.pdf`, `00002.pdf`, and so on, in order.

<Note>
  Each part is packed to just under `maximum_bytes` by rendered output size, so
  parts approach but never exceed the limit. The exception is a single page whose
  own size already exceeds `maximum_bytes`: it is returned as its own part that
  exceeds the limit, because a page is never split.
</Note>

<Tip>
  For end-to-end code that calls a split action and unpacks each format —
  extracting the ZIP, decoding the JSON envelope, or reading the multipart parts —
  see the [Splitting a PDF](/docs/api/splitting-a-pdf) guide.
</Tip>

## Errors

Failed requests return an `application/problem+json` body. The most common one
for this endpoint is a `400`, returned when `maximum_bytes` is missing or below
`1`, or when `file` isn't a readable PDF — the `errors` object names each field:

```json
{
  "type": "https://www.pdfblocks.com/docs/api/v1/error/400",
  "title": "One or more validation errors occurred.",
  "status": 400,
  "errors": {
    "maximum_bytes": ["The field maximum_bytes must be greater than or equal to 1."]
  }
}
```

If the `Accept` header matches none of `application/zip`, `application/json`, or
`multipart/mixed` — for example `Accept: application/pdf` — the API responds with
`406 Not Acceptable`. Omit `Accept` to take the ZIP default, or request one of the
supported media types. A missing or invalid `X-API-Key` returns a `401`. See
[Errors](/docs/api/errors) for every status code and the full response shape.

## Recipes

A common variation. Expand it to see the code in every language.

<AccordionGroup>

<Accordion title="Receive the parts as a JSON envelope">

Send `Accept: application/json` to get every part inline in one response, then
base64-decode each entry's `content` to a file named by its `name`:

<CodeGroup>

```bash title="cURL"
curl https://api.pdfblocks.com/v1/split_by_size \
  -H 'X-API-Key: your_api_key' \
  -H 'Accept: application/json' \
  -F file=@input.pdf \
  -F maximum_bytes=1048576 \
  | jq -r '.documents[] | .name + " " + .content' \
  | while read -r name content; do
      echo "$content" | base64 --decode > "$name"
    done
```

```python title="Python"
# pip install requests
import base64
import requests

with open('input.pdf', 'rb') as file:
    response = requests.post(
        'https://api.pdfblocks.com/v1/split_by_size',
        headers={
            'X-API-Key': 'your_api_key',
            'Accept': 'application/json',
        },
        files={'file': file},
        data={'maximum_bytes': 1048576},
    )

response.raise_for_status()
for document in response.json()['documents']:
    with open(document['name'], 'wb') as output:
        output.write(base64.b64decode(document['content']))
```

```javascript title="Node.js"
// Node.js 18+
import { readFile, writeFile } from 'node:fs/promises';

const body = new FormData();
body.set('file', new Blob([await readFile('input.pdf')]), 'input.pdf');
body.set('maximum_bytes', '1048576');

const response = await fetch('https://api.pdfblocks.com/v1/split_by_size', {
  method: 'POST',
  headers: { 'X-API-Key': 'your_api_key', Accept: 'application/json' },
  body,
});

if (!response.ok) throw new Error(`Request failed: ${response.status}`);
const { documents } = await response.json();
for (const doc of documents) {
  await writeFile(doc.name, Buffer.from(doc.content, 'base64'));
}
```

```php title="PHP"
<?php
$ch = curl_init('https://api.pdfblocks.com/v1/split_by_size');
curl_setopt_array($ch, [
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER => [
        'X-API-Key: your_api_key',
        'Accept: application/json',
    ],
    CURLOPT_POST => true,
    CURLOPT_POSTFIELDS => [
        'file' => new CURLFile('input.pdf', 'application/pdf'),
        'maximum_bytes' => '1048576',
    ],
]);

$body = curl_exec($ch);
if (curl_getinfo($ch, CURLINFO_HTTP_CODE) === 200) {
    foreach (json_decode($body, true)['documents'] as $document) {
        file_put_contents($document['name'], base64_decode($document['content']));
    }
}
```

```ruby title="Ruby"
# gem install http
require 'base64'
require 'http'
require 'json'

response = HTTP
  .headers('X-API-Key' => 'your_api_key', 'Accept' => 'application/json')
  .post('https://api.pdfblocks.com/v1/split_by_size', form: {
    file: HTTP::FormData::File.new('input.pdf'),
    maximum_bytes: '1048576',
  })

if response.status.success?
  JSON.parse(response.body)['documents'].each do |document|
    File.write(document['name'], Base64.decode64(document['content']))
  end
end
```

```go title="Go"
package main

import (
	"bytes"
	"encoding/base64"
	"encoding/json"
	"io"
	"mime/multipart"
	"net/http"
	"os"
)

func main() {
	var buf bytes.Buffer
	form := multipart.NewWriter(&buf)

	file, _ := os.Open("input.pdf")
	defer file.Close()
	part, _ := form.CreateFormFile("file", "input.pdf")
	io.Copy(part, file)

	form.WriteField("maximum_bytes", "1048576")
	form.Close()

	req, _ := http.NewRequest("POST", "https://api.pdfblocks.com/v1/split_by_size", &buf)
	req.Header.Set("Content-Type", form.FormDataContentType())
	req.Header.Set("X-API-Key", "your_api_key")
	req.Header.Set("Accept", "application/json")

	res, _ := http.DefaultClient.Do(req)
	defer res.Body.Close()

	var result struct {
		Documents []struct {
			Name    string `json:"name"`
			Content string `json:"content"`
		} `json:"documents"`
	}
	json.NewDecoder(res.Body).Decode(&result)

	for _, doc := range result.Documents {
		data, _ := base64.StdEncoding.DecodeString(doc.Content)
		os.WriteFile(doc.Name, data, 0644)
	}
}
```

```csharp title="C#"
using System.Text.Json;

using var client = new HttpClient();
client.DefaultRequestHeaders.Add("X-API-Key", "your_api_key");
client.DefaultRequestHeaders.Add("Accept", "application/json");

using var form = new MultipartFormDataContent
{
    { new ByteArrayContent(File.ReadAllBytes("input.pdf")), "file", "input.pdf" },
    { new StringContent("1048576"), "maximum_bytes" },
};

var response = await client.PostAsync(
    "https://api.pdfblocks.com/v1/split_by_size", form);
response.EnsureSuccessStatusCode();

using var json = JsonDocument.Parse(
    await response.Content.ReadAsStringAsync());
foreach (var document in json.RootElement.GetProperty("documents").EnumerateArray())
{
    var name = document.GetProperty("name").GetString()!;
    var content = document.GetProperty("content").GetString()!;
    await File.WriteAllBytesAsync(name, Convert.FromBase64String(content));
}
```

</CodeGroup>

</Accordion>

</AccordionGroup>

## Related actions

<CardGroup cols={2}>

<Card title="Split by page count" href="/docs/api/split-pdf-by-page-count">
  Split by page count instead of bytes.
</Card>

<Card title="Split at page" href="/docs/api/split-pdf-at-page">
  Split into two documents at a boundary.
</Card>

<Card title="Split into page groups" href="/docs/api/split-pdf-into-page-groups">
  Define arbitrary page groups by hand.
</Card>

<Card title="Extract pages" href="/docs/api/extract-pages-from-pdf">
  Keep one range of pages.
</Card>

</CardGroup>