Add a document time-stamp

The Pdftools SDK lets you apply a time-stamp to a PDF document. This type of digital signature provides evidence that a document existed at a specific time, and that the content of the document has not changed since that time.

Quick start with a code sample

Get the full sample on GitHub: C, C#, Java, Python, and Visual Basic.

The time-stamp is provided by a time-stamp authority (TSA) that is configured in the cryptographic provider. In this example, the Built-In cryptographic provider is used to apply a time-stamp to a PDF document. A third-party time-stamp authority is configured in the cryptographic provider.

Steps to apply a digital time-stamp:

1. Initialize the Pdftools SDK license
2. Initialize the cryptographic provider
3. Connect to the time-stamp authority
4. Add the document time-stamp
5. Full example

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1. Initialize the Pdftools SDK license

Before you begin, Initialize the Pdftools SDK license.

2. Initialize the cryptographic provider

When using the Built-In cryptographic provider, you start the document time-stamp process by instantiating the Provider object. The Provider object exposes the methods of the cryptographic provider. The cryptographic provider manages certificates and private keys, and implements cryptographic algorithms.

.NET

// Create a session to the built-in cryptographic provider
using var session = new BuiltIn.Provider();

Java

// Create a session to the built-in cryptographic provider
Provider session = new Provider();

3. Connect to the time-stamp authority

For the Built-In and PKCS#11 cryptographic providers, a third-party time-stamp authority must be configured. To do this, you pass the URL of the time-stamp authority to the cryptographic provider and call the CreateTimestamp method.

.NET

// Create time-stamp configuration
session.TimestampUrl = timeStampUrl;
var timestamp = session.CreateTimestamp();

Java

// Create time-stamp configuration
session.setTimestampUrl(timeStampUrl);
TimestampConfiguration timestamp = session.createTimestamp();

4. Add the document time-stamp

After instantiating the Provider and preparing the time-stamp configuration, you are ready to apply the digital time-stamp to a document.

The input and output PDF documents are created as streams (in this example, as file streams). The Signer object is used to apply the digital time-stamp.

Non-critical processing errors raise a Warning event. It is recommended to listen for these events, and review the WarningCategory to determine if further action is needed.

.NET

// Open the input document
using var inStr = File.OpenRead(inPath);
using var inDoc = Document.Open(inStr);

// Create a stream for the output file
using var outStr = File.Create(outPath);

// Create the Signer object
Signer signer = new Signer();

// Create an event listener to listen for warning events that are raised and write them to console
signer.Warning += (s, e) => Console.WriteLine("Warning - {0}: {1}: {2}", e.Category, e.Context, e.Message);

// Add the document time-stamp
using var outDoc = signer.AddTimestamp(inDoc, timestamp, outStr);

Java

// Open input document
FileStream inStr = new FileStream(inPath, FileStream.Mode.READ_ONLY);
Document inDoc = Document.open(inStr);

// Create a stream for the output file
FileStream outStr = new FileStream(outPath, FileStream.Mode.READ_WRITE_NEW);

// Create the Signer object
Signer signer = new Signer();

// (optional) Create an event listener to listen for warning events that are raised and write them to console
signer.addWarningListener((e) -> { System.out.format("Warning - %s: %s: %s", e.getCategory(), e.getContext(), e.getMessage()); });

// Add the document time-stamp
Document outDoc = signer.addTimestamp(inDoc, timestamp, outStr);

Full example

The code snippets in the previous steps are excerpts that illustrate the workflow. They aren’t complete, runnable programs. Before you run Pdftools SDK, install the package for your language and set up a license key. For setup steps, see Getting started with Pdftools SDK.

For a complete, runnable project, clone the sample repository for your language and run the BuiltInAddTimestamp sample:

• C
• C#
• Java
• Python
• Visual Basic

Signature visual appearance

You can also apply a visual appearance to the signatures. For more information, see Create a signature visual appearance page.

Signing PDF/A documents

Converting a PDF to PDF/A removes any signatures from the file before archiving. Therefore, archive a file to PDF/A before you apply any digital signatures.