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Protecting and unlocking documents

Sequence the security actions — encrypt, set restrictions, remove a known password, clear restrictions — for a real document workflow.

PDF security is two separate things, and getting the order right depends on knowing which is which. A password encrypts the file and controls who can open it. Restrictions are permission flags that control what a reader can do once it is open — print, copy, edit. This guide sequences the five security actions into a protect-then-distribute flow and an unlock flow.

The security actions

Action Route What it does
Add password add_password Encrypts the PDF and sets the password needed to open it.
Add restrictions add_restrictions Sets permission flags (print, copy, edit) behind an owner password; can also set an open password.
Remove password remove_password Decrypts a PDF when you supply its current password.
Remove restrictions remove_restrictions Clears all permission flags.
Remove signatures remove_signatures Strips cryptographic signatures and timestamps.

Passwords vs. restrictions. add_password takes a single password — the password a reader types to open the file. add_restrictions takes an owner_password that guards the permission flags, plus an optional user_password that acts as the open password. Set user_password and the document needs a password to open; leave it out and anyone can open it but is still bound by the permission flags.

The one rule that governs the order

Encrypt last. An encrypted PDF can’t be opened by any other action, because there is no field to supply its password. So run every content and permission step first — merge, watermark, restrictions — and add the open password as the final step. To modify a document that is already password-protected, remove the password first, process it, then re-protect.

Because of that rule, don’t stack add_password and then add_restrictions — the restrictions call can’t open the just-encrypted file. When you need both an open password and permission flags, set them in a single add_restrictions call using owner_password and user_password together.

Protect a document for distribution

Lock down a report so it requires a password to open, and can’t be printed, copied, or edited — all in one call.

Prepare the content first

Do any merging, watermarking, or page work now, while the document is still unencrypted. See Chaining actions.

Apply restrictions and an open password

POST /v1/add_restrictions with an owner_password (guards the permissions), a user_password (the open password), and the permission flags set to false for what you want to forbid.

cURLbash
curl https://api.pdfblocks.com/v1/add_restrictions \
  -H 'X-API-Key: your_api_key' \
  -F file=@input.pdf \
  -F owner_password='owner-secret' \
  -F user_password='open-secret' \
  -F allow_print=false \
  -F allow_copy_content=false \
  -F allow_change_content=false \
  -o protected.pdf
Pythonpython
# pip install requests
import requests

with open('input.pdf', 'rb') as file:
    response = requests.post(
        'https://api.pdfblocks.com/v1/add_restrictions',
        headers={'X-API-Key': 'your_api_key'},
        files={'file': file},
        data={
            'owner_password': 'owner-secret',
            'user_password': 'open-secret',
            'allow_print': 'false',
            'allow_copy_content': 'false',
            'allow_change_content': 'false',
        },
    )

response.raise_for_status()
with open('protected.pdf', 'wb') as output:
    output.write(response.content)
Node.jsjavascript
// 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('owner_password', 'owner-secret');
body.set('user_password', 'open-secret');
body.set('allow_print', 'false');
body.set('allow_copy_content', 'false');
body.set('allow_change_content', 'false');

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

if (!response.ok) throw new Error(`Request failed: ${response.status}`);
await writeFile('protected.pdf', Buffer.from(await response.arrayBuffer()));
PHPphp
<?php
$ch = curl_init('https://api.pdfblocks.com/v1/add_restrictions');
curl_setopt_array($ch, [
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER => ['X-API-Key: your_api_key'],
    CURLOPT_POST => true,
    CURLOPT_POSTFIELDS => [
        'file' => new CURLFile('input.pdf', 'application/pdf'),
        'owner_password' => 'owner-secret',
        'user_password' => 'open-secret',
        'allow_print' => 'false',
        'allow_copy_content' => 'false',
        'allow_change_content' => 'false',
    ],
]);

$pdf = curl_exec($ch);
if (curl_getinfo($ch, CURLINFO_HTTP_CODE) === 200) {
    file_put_contents('protected.pdf', $pdf);
}
Rubyruby
# gem install http
require 'http'

response = HTTP
  .headers('X-API-Key' => 'your_api_key')
  .post('https://api.pdfblocks.com/v1/add_restrictions', form: {
    file: HTTP::FormData::File.new('input.pdf'),
    owner_password: 'owner-secret',
    user_password: 'open-secret',
    allow_print: 'false',
    allow_copy_content: 'false',
    allow_change_content: 'false',
  })

File.write('protected.pdf', response.body) if response.status.success?
Gogo
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("owner_password", "owner-secret")
	form.WriteField("user_password", "open-secret")
	form.WriteField("allow_print", "false")
	form.WriteField("allow_copy_content", "false")
	form.WriteField("allow_change_content", "false")
	form.Close()

	req, _ := http.NewRequest("POST",
		"https://api.pdfblocks.com/v1/add_restrictions", &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("protected.pdf")
	defer out.Close()
	io.Copy(out, res.Body)
}
C#csharp
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("owner-secret"), "owner_password" },
    { new StringContent("open-secret"), "user_password" },
    { new StringContent("false"), "allow_print" },
    { new StringContent("false"), "allow_copy_content" },
    { new StringContent("false"), "allow_change_content" },
};

var response = await client.PostAsync(
    "https://api.pdfblocks.com/v1/add_restrictions", form);
response.EnsureSuccessStatusCode();
await File.WriteAllBytesAsync(
    "protected.pdf", await response.Content.ReadAsByteArrayAsync());

If you only need an open password and no permission flags, add_password is the simpler call:

cURLbash
curl https://api.pdfblocks.com/v1/add_password \
  -H 'X-API-Key: your_api_key' \
  -F file=@input.pdf \
  -F password='pa$$word' \
  -o encrypted.pdf

Both add_password and add_restrictions accept an encryption_algorithm of AES-128 (the default) or AES-256. See Add password and Add restrictions for every field.

Unlock a document

To lift protection you hold the credentials for, decrypt first, then clear the permission flags.

Remove the open password

POST /v1/remove_password with the document’s current password. The result no longer requires a password to open, so later steps can read it.

Clear the restrictions

POST /v1/remove_restrictions strips the permission flags, leaving an unrestricted PDF.

cURLbash
# 1. Decrypt with the known password.
curl -sS https://api.pdfblocks.com/v1/remove_password \
  -H 'X-API-Key: your_api_key' \
  -F file=@protected.pdf \
  -F password='open-secret' |
# 2. Clear the permission flags from the decrypted bytes.
curl -sS https://api.pdfblocks.com/v1/remove_restrictions \
  -H 'X-API-Key: your_api_key' \
  -F 'file=@-;filename=unlocked.pdf;type=application/pdf' \
  -o unrestricted.pdf
Pythonpython
# pip install requests
import requests

BASE = 'https://api.pdfblocks.com'
HEADERS = {'X-API-Key': 'your_api_key'}

# 1. Decrypt with the known password.
with open('protected.pdf', 'rb') as file:
    unlocked = requests.post(
        f'{BASE}/v1/remove_password',
        headers=HEADERS,
        files={'file': file},
        data={'password': 'open-secret'},
    )
unlocked.raise_for_status()

# 2. Clear the permission flags from the decrypted bytes.
unrestricted = requests.post(
    f'{BASE}/v1/remove_restrictions',
    headers=HEADERS,
    files={'file': ('unlocked.pdf', unlocked.content, 'application/pdf')},
)
unrestricted.raise_for_status()

with open('unrestricted.pdf', 'wb') as output:
    output.write(unrestricted.content)

remove_restrictions has no password field, so it works on a document that is restricted but not password-protected. If a document has an open password, run remove_password first — as the flow above does — so the restrictions call can read it.

Remove signatures

A cryptographic signature locks a PDF: any edit invalidates it. If you must re-process a signed document, strip the signatures and timestamps first with remove_signatures. This does invalidate the signatures — which is unavoidable once the content changes.

cURLbash
curl https://api.pdfblocks.com/v1/remove_signatures \
  -H 'X-API-Key: your_api_key' \
  -F file=@signed.pdf \
  -o unsigned.pdf
Add a password

Encrypt a PDF with an open password.

Add restrictions

Set the full permission-flag matrix.

Remove a password

Decrypt a PDF you have the password for.

Chaining actions

Watermark or merge before you encrypt.