1. Install Required Libraries

 pip install PyPDF2 cryptography pikepdf

2. Basic Verification with PyPDF2

    from PyPDF2 import PdfReader

# Load the PDF
file_path = "signed_document.pdf"
reader = PdfReader(file_path)

# Check for signature fields
fields = reader.get_fields()
if fields:
    print("Fields detected:")
    for field_name, field_data in fields.items():
        print(f"Field: {field_name}, Data: {field_data}")
else:
    print("No signature fields detected.")

3. Advanced Verification with PdfSig

    sudo apt install poppler-utils

    import subprocess

file_path = "signed_document.pdf"

# Run pdfsig command
result = subprocess.run(["pdfsig", file_path], capture_output=True, text=True)

# Output the verification results
if result.returncode == 0:
    print("Verification Details:")
    print(result.stdout)
else:
    print("Error verifying signature.")
    print(result.stderr)

4. Using Cryptography Library

    from cryptography.hazmat.primitives.asymmetric import padding
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.primitives.serialization import load_pem_public_key

# Example of signature and public key (you must extract these from the PDF)
signature = b"..."
public_key_data = b"""-----BEGIN PUBLIC KEY-----
...
-----END PUBLIC KEY-----"""

message = b"original_message_to_verify"  # Extract the exact signed data

# Load public key
public_key = load_pem_public_key(public_key_data)

# Verify signature
try:
    public_key.verify(
        signature,
        message,
        padding.PKCS1v15(),
        hashes.SHA256()
    )
    print("Signature is valid.")
except Exception as e:
    print(f"Signature verification failed: {e}")

5. Third-party Libraries/Tools

   pip install pyhanko
   Example: from pyhanko.sign.validation import validate_pdf_signature

   with open(“signed_document.pdf”, “rb”) as doc:
   validation_results = validate_pdf_signature(doc)

   for res in validation_results:
   print(res)