# Digital Signatures > Sign PDF and PDF/A documents with TX Text Control .NET Server: certificates, signature fields, PAdES, RFC 3161 timestamps, several signers and validation. - **Product:** TX Text Control .NET Server - **Section:** Documentation - **Kind:** Topic - **Path:** TX Text Control .NET Server > Digital Signatures - **906 words** - **Web URL:** https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/ - **LLMs URL:** https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/llms.txt - **LLMs-Full URL:** https://docs.textcontrol.com/tx-text-control-dotnet-server/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 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](https://docs.textcontrol.com/tx-text-control-dotnet-server/getting-started/pdf/sign/llms-full.txt) in Getting Started creates a test certificate and signs a first document in a few steps. ### How Signing Works in TX Text Control 1. **A certificate.** Your code loads an X.509 certificate with its private key as a .NET `X509Certificate2` and wraps it in a `DigitalSignature`, optionally with the URL of a time server for a trusted timestamp. 2. **The place of the signature.** `SaveSettings.DigitalSignature` signs the whole document with an invisible signature. `SaveSettings.SignatureFields` signs named signature fields, each with its own certificate and a visible image. 3. **The save.** The signature is created when `ServerTextControl` saves the document as PDF or PDF/A. Any change after that invalidates it. 4. **The check.** PDF readers such as Adobe Acrobat Reader show whether a signature is valid, and the `TXTextControl.PDF.Validation` package 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](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/overview/llms-full.txt) | | Sign merged or converted documents, return signed PDF documents from ASP.NET Core and handle errors | [Signing PDF Documents](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/signing/llms-full.txt) | | Load certificates from files, the Windows certificate store or Azure Key Vault | [Certificate-Based Signatures](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/certificate-based/llms-full.txt) | | Create, read and sign signature fields with images and signer data | [Signature Fields](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/signature-fields/llms-full.txt) | | Understand the PAdES profiles and electronic signature levels | [PAdES](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/pades/llms-full.txt) | | Add trusted timestamps and handle unavailable time servers | [RFC 3161 Timestamps](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/timestamps/llms-full.txt) | | Sign a document for several people or with several certificates | [Multiple Signatures](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/multiple/llms-full.txt) | | Check the signatures of PDF documents in code | [Signature Validation](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/validation/llms-full.txt) | | Create certificates for development and tests | [Self-Signed Certificates](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/self-signed/llms-full.txt) | ### Where to Start 1. [Overview](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/overview/llms-full.txt): the concepts and the building blocks. 2. [Self-Signed Certificates](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/self-signed/llms-full.txt): a certificate to develop with. 3. [Signing PDF Documents](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/signing/llms-full.txt) or [Signature Fields](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/signature-fields/llms-full.txt), depending on whether the whole document or single fields are signed. 4. [Signature Validation](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/validation/llms-full.txt): check the result. ### Related Sections - [Digital Signatures](https://docs.textcontrol.com/tx-text-control-dotnet-server/document-viewer/digital-signatures/llms-full.txt) in Document Viewer: collect signatures from users in the browser. - [Signature Fields](https://docs.textcontrol.com/tx-text-control-dotnet-server/document-editor/signature-fields/llms-full.txt) in Document Editor: design documents for signing. - [PDF Processing](https://docs.textcontrol.com/tx-text-control-dotnet-server/pdf/llms-full.txt): create PDF/A documents, protect them with passwords and add attachments. - [Digital Signatures](https://docs.textcontrol.com/tx-text-control-dotnet-server/security/signatures/llms-full.txt) in Security: security aspects of signing. --- ## In This Section - [Certificate-Based Signatures](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/certificate-based/llms-full.txt): Sign PDF documents with X.509 certificates: requirements, DigitalSignature, PFX data, the Windows certificate store, Azure Key Vault and certificate checks. - [Multiple Signatures](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/multiple/llms-full.txt): Sign all signature fields of a PDF in one save: a DigitalSignature per field, several certificates and timestamps, sequential signers in the Document Viewer. - [Overview](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/overview/llms-full.txt): Integrity and authenticity of signed PDFs explained: signing versus encryption, electronic versus digital signatures, DigitalSignature and server workflows. - [PAdES](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/pades/llms-full.txt): PAdES signature profiles for PDF documents: PAdES-B and PAdES-T, what TX Text Control creates, eIDAS signature levels, PDF/A and checking signed documents. - [Self-Signed Certificates](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/self-signed/llms-full.txt): Create self-signed test certificates for PDF signatures with PowerShell, OpenSSL or Acrobat Reader, use them in your project and move to CA certificates. - [Signature Fields](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/signature-fields/llms-full.txt): Create, read and sign signature fields with ServerTextControl: SignatureField, positions, SignatureImage, SignerData, MS Word signature lines and PDF output. - [Signing PDF Documents](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/signing/llms-full.txt): Sign the whole PDF or PDF/A document with DigitalSignature and SaveSettings: merged documents, byte arrays, ASP.NET Core, errors and what happens after signing. - [RFC 3161 Timestamps](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/timestamps/llms-full.txt): Add trusted RFC 3161 timestamps to PDF signatures: time-stamping authorities, the timeServerURL parameter, InvalidTimeServer errors and signature fields. - [Signature Validation](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/validation/llms-full.txt): Validate the signatures of PDF documents with TXTextControl.PDF.Validation: signature diagnostics, what they check, rejecting uploads and testing tampering. --- ## Nearby - **Previous:** [PDF Validation](https://docs.textcontrol.com/tx-text-control-dotnet-server/pdf/validation/llms-full.txt) - **Next:** [Overview](https://docs.textcontrol.com/tx-text-control-dotnet-server/digital-signatures/overview/llms-full.txt)