Digital Signatures
Who signed this document, and has anybody changed it since? Digital signatures answer both questions inside the PDF itself, where every recipient can check them. TX Text Control .NET Server signs PDF and PDF/A documents while it saves them, for the whole document or for single signature fields. It works together with the Document Viewer, which collects the signatures of users in the browser. The pages below lead from the concepts to certificates, timestamps, processes with several signers and validation.
Digitally Sign a PDF in Getting Started creates a test certificate and signs a first document in a few steps.
How Signing Works in TX Text Control
- A certificate. Your code loads an X.509 certificate with its private key as a .NET
X509Certificate2and wraps it in aDigitalSignature, optionally with the URL of a time server for a trusted timestamp. - The place of the signature.
SaveSettings.DigitalSignaturesigns the whole document with an invisible signature.SaveSettings.SignatureFieldssigns named signature fields, each with its own certificate and a visible image. - The save. The signature is created when
ServerTextControlsaves the document as PDF or PDF/A. Any change after that invalidates it. - The check. PDF readers such as Adobe Acrobat Reader show whether a signature is valid, and the
TXTextControl.PDF.Validationpackage checks its integrity in code.
Signature fields are placed in documents by users in the Document Editor or by your code, and users sign them electronically in the Document Viewer before the server applies the certificates.
Find the Right Page
| If you want to | Read |
|---|---|
| Understand what signatures prove, how electronic and digital signatures differ and which parts of TX Text Control take part | Overview |
| Sign merged or converted documents, return signed PDF documents from ASP.NET Core and handle errors | Signing PDF Documents |
| Load certificates from files, the Windows certificate store or Azure Key Vault | Certificate-Based Signatures |
| Create, read and sign signature fields with images and signer data | Signature Fields |
| Understand the PAdES profiles and electronic signature levels | PAdES |
| Add trusted timestamps and handle unavailable time servers | RFC 3161 Timestamps |
| Sign a document for several people or with several certificates | Multiple Signatures |
| Check the signatures of PDF documents in code | Signature Validation |
| Create certificates for development and tests | Self-Signed Certificates |
Where to Start
- Overview: the concepts and the building blocks.
- Self-Signed Certificates: a certificate to develop with.
- Signing PDF Documents or Signature Fields, depending on whether the whole document or single fields are signed.
- Signature Validation: check the result.