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

Download the full sample now in C# and Java.

Interested in C or other language samples? Let us know on the contact page and we'll add it to our samples backlog.

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 cryptographic provider.
2. Connect to the time-stamp authority.
3. Add the document time-stamp.

---

Before you begin

You need to initialize the library.

Initializing 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();

Connecting 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();

Adding 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 = new 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()); });

// Sign the input document
Document outDoc = signer.addTimestamp(inDoc, signature, outStr);

Full example

.NET

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

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

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

// Create stream for 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

// Create a session to the built-in cryptographic provider
try (Provider session = new Provider())
{
    // Configure URL of the trusted time-stamp authority (TSA)
    session.setTimestampUrl(timeStampUrl);

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

    // 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()); });

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

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

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

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

During the conversion process from PDF to PDF/A, any signatures are removed from the file before it is converted to PDF/A for archival. Therefore we recommend files that require archiving should be archived to PDF/A format before any digital signatures are applied.