How to Sign PDFs Using Digital Certificates in Python

A complete Python tutorial showing how to digitally sign PDF files using .pfx or .p12 certificates with the PDFSignify API.

This guide covers:

• Sign PDFs in Python
• Upload .pfx / .p12 certificates
• Use the PDFSignify REST API
• Customize PDF signatures
• Add metadata to signed PDFs
• Save signed PDFs automatically

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Table of Contents

• Introduction
• 1. Create the Python Project
• 2. Create a Virtual Environment
• 3. Install Dependencies
• 4. Create a PDFSignify Account
• 5. Create API Credentials
• 6. Prepare the PDF and Certificate
• 7. Sign PDFs in Python
• 8. Customize the Signature
• 9. Add PDF Metadata
• 10. Complete Example

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Introduction

This tutorial explains how to digitally sign PDF documents using Python and PDFSignify.

Digital signatures help verify:

• document authenticity
• document integrity
• signer identity

You need:

• a PDF file
• a .pfx or .p12 certificate
• the certificate password
• PDFSignify API credentials

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1. Create the Python Project

mkdir python-pdf-signing
cd python-pdf-signing

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2. Create a Virtual Environment

Create the virtual environment:

python3 -m venv venv

Activate it on Linux/macOS:

source venv/bin/activate

Activate it on Windows:

venv\Scripts\activate

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3. Install Dependencies

Install requests:

pip install requests

Optional:

pip freeze > requirements.txt

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4. Create a PDFSignify Account

Go to:

https://pdfsignify.com/

Create an account or log in.

Verify your email:

If needed, resend the verification email:

Create a project:

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5. Create API Credentials

Open the API credentials section.

Create credentials:

Save:

• AccessKey
• SecretKey

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6. Prepare the PDF and Certificate

Project structure:

python-pdf-signing/
├── sign_pdf.py
├── filepdf.pdf
├── certificate.pfx
└── venv/

Supported certificate formats:

• .pfx
• .p12

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7. Sign PDFs in Python

Create sign_pdf.py:

import requests

API_URL = "https://api.pdfsignify.com/api/v1/sign-pdf"

ACCESS_KEY = "MY_ACCESS_KEY"
SECRET_KEY = "MY_SECRET_KEY"

CERTIFICATE_PATH = "certificate.pfx"
PDF_PATH = "filepdf.pdf"

CERTIFICATE_PASSWORD = "YOUR_CERTIFICATE_PASSWORD"

headers = {
    "AccessKey": ACCESS_KEY,
    "SecretKey": SECRET_KEY,
}

data = {
    "certificatePassword": CERTIFICATE_PASSWORD,
}

with open(CERTIFICATE_PATH, "rb") as certificate_file, open(PDF_PATH, "rb") as pdf_file:

    files = {
        "certificate": (
            "certificate.pfx",
            certificate_file,
            "application/x-pkcs12"
        ),

        "pdf": (
            "filepdf.pdf",
            pdf_file,
            "application/pdf"
        ),
    }

    response = requests.post(
        API_URL,
        headers=headers,
        files=files,
        data=data
    )

if response.status_code != 200:
    print("Error signing PDF")
    print(response.text)
    exit(1)

with open("signed_filepdf.pdf", "wb") as signed_pdf:
    signed_pdf.write(response.content)

print("PDF signed successfully")

Run the script:

python sign_pdf.py

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8. Customize the Signature

Example signature configuration:

data = {
    "certificatePassword": CERTIFICATE_PASSWORD,

    "signaturePageAppearance": "-1",
    "timezone": "UTC",

    "signatureMessage": "Digitally signed by the user",

    "signatureDateFormat": "Y-m-d H:i:s",

    "signatureHeight": "100",
    "signatureWidth": "150",

    "signatureYPosition": "100",
    "signatureXPosition": "180",
}

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9. Add PDF Metadata

data = {
    "certificatePassword": CERTIFICATE_PASSWORD,

    "pdfMetadataAuthor": "AUTHOR",
    "pdfMetadataKeywords": "keywords,keyword2",

    "pdfMetadataTitle": "MY DOCUMENT",
    "pdfMetadataSubject": "EXAMPLE DOCUMENT",

    "pdfMetadataCreator": "PDFSIGNIFY",
    "pdfMetadataProducer": "PDFSIGNIFY",
}

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10. Complete Example

import requests
from datetime import datetime

API_URL = "https://api.pdfsignify.com/api/v1/sign-pdf"

ACCESS_KEY = "MY_ACCESS_KEY"
SECRET_KEY = "MY_SECRET_KEY"

CERTIFICATE_PATH = "certificate.pfx"
PDF_PATH = "filepdf.pdf"

CERTIFICATE_PASSWORD = "YOUR_CERTIFICATE_PASSWORD"

OUTPUT_PATH = "signed_filepdf.pdf"

headers = {
    "AccessKey": ACCESS_KEY,
    "SecretKey": SECRET_KEY,
}

current_datetime = datetime.now().strftime("%Y-%m-%d %H:%M:%S")

data = {
    "certificatePassword": CERTIFICATE_PASSWORD,

    "signaturePageAppearance": "-1",
    "timezone": "UTC",

    "signatureMessage": "Digitally signed by the user",

    "signatureDateFormat": "Y-m-d H:i:s",

    "signatureHeight": "100",
    "signatureWidth": "150",

    "signatureYPosition": "100",
    "signatureXPosition": "180",

    "pdfMetadataAuthor": "AUTHOR",
    "pdfMetadataKeywords": "keywords,keyword2",

    "pdfMetadataTitle": "MY DOCUMENT",
    "pdfMetadataSubject": "EXAMPLE DOCUMENT",

    "pdfMetadataCreator": "PDFSIGNIFY",
    "pdfMetadataProducer": "PDFSIGNIFY",

    "pdfMetadataCreationDate": current_datetime,
    "pdfMetadataModificationDate": current_datetime,
}

with open(CERTIFICATE_PATH, "rb") as certificate_file, open(PDF_PATH, "rb") as pdf_file:

    files = {
        "certificate": (
            "certificate.pfx",
            certificate_file,
            "application/x-pkcs12"
        ),

        "pdf": (
            "filepdf.pdf",
            pdf_file,
            "application/pdf"
        ),
    }

    response = requests.post(
        API_URL,
        headers=headers,
        files=files,
        data=data
    )

if response.status_code != 200:
    print("Error signing PDF")
    print(response.text)
    exit(1)

with open(OUTPUT_PATH, "wb") as signed_pdf:
    signed_pdf.write(response.content)

print(f"PDF signed successfully: {OUTPUT_PATH}")

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Useful Links

• https://pdfsignify.com/
• https://api.pdfsignify.com/api/documentation#/

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License

MIT