Add a Timestamped Digital Signature to PDF in Python

Introduction

Digital signatures help verify the authenticity and integrity of PDF documents. However, if a signing certificate expires or is revoked, the signature alone may no longer be considered valid. To solve this, a timestamp can be added to the digital signature, proving that the document was signed at a specific point in time-validated by a trusted Time Stamp Authority (TSA).

In this tutorial, we will introduce how to use the Spire.PDF for Python library to digitally sign a PDF document with a timestamp in Python.

Prerequisites

To follow this tutorial, ensure you have the following:

• Spire.PDF for Python library
You can install Spire.PDF for Python via pip:
• Package Manager

pip install Spire.PDF

If you are unsure how to install, please refer to this tutorial: How to Install Spire.PDF for Python on Windows
• A valid digital certificate (.pfx file)
This certificate is used to create the digital signature.
• A sample PDF file
This is the document you want to sign.
• An image to display as the signature appearance (optional)
For visual representation of the signer.
• A reliable Time Stamp Authority (TSA) URL
This provides the timestamp token during signing.

How to Digitally Sign a PDF with a Timestamp in Python

In Spire.PDF for Python, the Security_PdfSignature class is used to create a digital signature, and the ConfigureTimestamp(tsaUrl) method in this class is used to embed a timestamp into the signature. The tsaUrl parameter specifies the address of the TSA server.

Steps to Add a Timestamped Digital Signature

Follow these steps to add a timestamped digital signature to a PDF in Python using Spire.PDF for Python:

• Create a PdfDocument instance and use the LoadFromFile() method to load the PDF you want to sign.
• Create a Security_PdfSignature object, specifying the target page, certificate file path, certificate password, and signature name.
• Configure the signature's appearance, including its position, size, display labels, and signature image.
• Embed a timestamp by calling the ConfigureTimestamp(tsaUrl) method with a valid Time Stamp Authority (TSA) URL.
• Save the signed PDF using the SaveToFile() method.

Code Example

from spire.pdf import *

inputFile = "Sample.pdf"
inputFile_pfx = "gary.pfx"
inputImage = "E-iceblueLogo.png"
outputFile = "SignWithTimestamp.pdf"

# Create a PdfDocument instance and load the PDF file to be signed
doc = PdfDocument()
doc.LoadFromFile(inputFile)

# Create a digital signature object by specifying the document, target page, certificate file path, certificate password, and signature name
signature = Security_PdfSignature(doc, doc.Pages.get_Item(0), inputFile_pfx, "e-iceblue", "signature")

# Define the position and size of the signature on the page (unit: point)
signature.Bounds = RectangleF(PointF(90.0, 600.0), SizeF(180.0, 90.0))

# Set the labels and content for the signature details
signature.NameLabel = "Digitally signed by: "
signature.Name = "Gary"
signature.LocationInfoLabel = "Location: "
signature.LocationInfo = "CN"
signature.ReasonLabel = "Reason: "
signature.Reason = "Ensure authenticity"
signature.ContactInfoLabel = "Contact Number: "
signature.ContactInfo = "028-81705109"

# Set document permissions: allow form filling, forbid further changes
signature.DocumentPermissions = PdfCertificationFlags.AllowFormFill.value | PdfCertificationFlags.ForbidChanges.value

# Set the graphic mode to include both image and signature details,
# and set the signature image
signature.GraphicsMode = Security_GraphicMode.SignImageAndSignDetail
signature.SignImageSource = PdfImage.FromFile(inputImage)

# Embed a timestamp into the signature using a Time Stamp Authority (TSA) server
url = "http://tsa.cesnet.cz:3161/tsa"
signature.ConfigureTimestamp(url)

# Save the signed PDF and close the document
doc.SaveToFile(outputFile)
doc.Close()

View the Timestamp in PDF

When you open the signed PDF in a viewer like Adobe Acrobat, you can click the Signature Panel to view both the digital signature and the timestamp, which confirm the document’s validity and the signing time:

Get a Free License

To fully experience the capabilities of Spire.PDF for Python without any evaluation limitations, you can request a free 30-day trial license.

Conclusion

Timestamping enhances the reliability of digital signatures by proving when a PDF was signed-even after the certificate has expired. With Spire.PDF for Python, implementing a timestamped digital signature is a straightforward process. Whether you're handling contracts, invoices, or confidential records, this approach ensures long-term document validity and compliance.