How to sign a PDF on laptop—do I need an electronic or digital signature?

pyHanko is a free tool for certificate-based PDF signing. If you’re comfortable running a Python script, you can sign locally without uploading your document.

You’ll need a .p12 or .pfx file containing your signing certificate and private key. Install the library first:

python -m pip install pyHanko

Put input.pdf and your certificate, here named certificate.pfx, in the same folder as this script. Save it as sign_pdf.py:

from getpass import getpass

from pyhanko.sign import signers
from pyhanko.pdf_utils.incremental_writer import IncrementalPdfFileWriter

signer = signers.SimpleSigner.load_pkcs12(
      "certificate.pfx",
      passphrase=getpass("Certificate password: ").encode("utf-8"),
)

if signer is None:
     raise RuntimeError("Unable to load the certificate and private key.")

with open("input.pdf", "rb") as source:
        with open("signed.pdf", "wb") as destination:
               signers.sign_pdf(
                     IncrementalPdfFileWriter(source),
                     signature_meta=signers.PdfSignatureMetadata(
                           field_name="Signature1"
                     ),
                     signer=signer,
                     output=destination,
                )
print("Created signed.pdf")

Run it from that folder:

python sign_pdf.py

This adds a digital signature without a visible handwritten image. Open signed.pdf in a reader with signature validation to check it.

The signing operation works offline. However, a self-signed certificate may show as untrusted on someone else’s computer. If the recipient requires a trusted certificate, confirm what they accept before obtaining one.