# Digital Signatures > Sign PDF and PDF/A documents in Windows Forms: certificates from files or the Windows store, signature fields, several signers and RFC 3161 timestamps. - **Product:** TX Text Control .NET for Windows Forms - **Section:** Documentation - **Kind:** Topic - **Path:** TX Text Control .NET for Windows Forms > Digital Signatures - **775 words** - **Web URL:** https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/ - **LLMs URL:** https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/llms.txt - **LLMs-Full URL:** https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/llms-full.txt --- 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 for Windows Forms signs PDF and PDF/A documents while it saves them, either the whole document or single signature fields, with a certificate from a file or from the Windows certificate store. The pages below lead from the concepts to certificates, visible signatures, several signers and trusted timestamps. Signing for the first time? [Digitally Sign a PDF](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/getting-started/pdf/sign/llms-full.txt) in Getting Started creates a test certificate and signs a document from a form in a few steps. ### How Signing Works in TX Text Control Your code wraps an X.509 certificate with its private key in a `DigitalSignature`, and `TextControl` or `ServerTextControl` signs the whole document or named signature fields while it saves the document as PDF or PDF/A. [The Building Blocks](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/overview/#the-building-blocks) in the Overview lists the classes that take part, and [How Signing Works in TX Text Control](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/signing/#how-signing-works-in-tx-text-control) the formats and `Save` overloads that sign. ### Find the Right Page | If you want to | Read | |---|---| | Understand what a signature proves, how electronic and digital signatures differ and which parts of TX Text Control take part | [Overview](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/overview/llms-full.txt) | | Sign the document of the editor or a merged document, sign into memory, handle errors and verify signatures in code | [Signing PDF Documents](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/signing/llms-full.txt) | | Load certificates from *.pfx* files, let users choose one from the Windows certificate store and check them | [Certificates](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/certificates/llms-full.txt) | | Sign signature fields, give them images and generate a signature appearance | [Signature Fields and Signature Appearance](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/signature-fields/llms-full.txt) | | Sign a document for several people or with several certificates | [Multiple Signatures](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/multiple/llms-full.txt) | | Add trusted timestamps, handle unavailable time servers and create PAdES-T signatures | [Timestamp Configuration](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/timestamps/llms-full.txt) | ### Where to Start 1. [Overview](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/overview/llms-full.txt): the concepts and the building blocks. 2. [Certificates](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/certificates/llms-full.txt): a certificate to develop with and the certificates of your users. 3. [Signing PDF Documents](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/signing/llms-full.txt) or [Signature Fields and Signature Appearance](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/signature-fields/llms-full.txt), depending on whether the whole document or single fields are signed. 4. [Timestamp Configuration](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/timestamps/llms-full.txt): keep the signatures verifiable for years. ### Related Sections - [Signature Fields](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/document-editor/signature-fields/llms-full.txt) in Document Editor: insert signature fields and edit their signer data in the editor. - [PDF Processing](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/pdf/llms-full.txt): create PDF/A documents, protect them with passwords and export forms. - [Certificate and Private Key Handling](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/security/certificates/llms-full.txt) in Security: protect certificates and their private keys. - [Digital Signature Examples](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/examples/digital-signatures/llms-full.txt): sample projects and blog articles with code. --- ## In This Section - [Certificates](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/certificates/llms-full.txt): Load X.509 signing certificates in Windows Forms from PFX files or the Windows certificate store, let users pick one with X509Certificate2UI and check it. - [Multiple Signatures](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/multiple/llms-full.txt): Sign one PDF for several people in Windows Forms: one DigitalSignature per signature field, different certificates, sequential signers and a final save. - [Overview](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/overview/llms-full.txt): Digital and electronic signatures in Windows Forms compared: integrity, authenticity, whole-document or field signatures, DigitalSignature and workflows. - [Signature Fields and Signature Appearance](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/signature-fields/llms-full.txt): Sign the named SignatureField frames of a Windows Forms TextControl: SignerData, a SignatureImage and how it's saved, the layout dialog and an SVG stamp. - [Signing PDF Documents](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/signing/llms-full.txt): Sign the TextControl document or a merged invoice as PDF in Windows Forms with DigitalSignature, handle FilterException and verify the signatures in code. - [Timestamp Configuration](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/timestamps/llms-full.txt): Configure RFC 3161 timestamps for PDF signatures in Windows Forms: the timeServerURL parameter, fallback servers, InvalidTimeServer, fields and PAdES-T. --- ## Nearby - **Previous:** [Passwords and Access Permissions](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/pdf/passwords/llms-full.txt) - **Next:** [Overview](https://docs.textcontrol.com/tx-text-control-dotnet-winforms/digital-signatures/overview/llms-full.txt)