# Overview > What a PDF signature proves and what it doesn't, electronic and digital signatures, and the WPF parts: DigitalSignature, SignatureField and the ribbon tabs. - **Product:** TX Text Control .NET for WPF - **Section:** Documentation - **Kind:** Topic - **Path:** TX Text Control .NET for WPF > Digital Signatures > Overview - **1735 words** - **Web URL:** https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/overview/ - **LLMs URL:** https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/overview/llms.txt - **LLMs-Full URL:** https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/overview/llms-full.txt --- A signed PDF document carries its own proof: of who signed it, and that nobody changed it afterward. Any recipient can check that proof in a PDF reader, without access to your application or your systems. TX Text Control .NET for WPF creates such signatures when it saves a document as PDF, whether the document comes from the `TextControl` in your window or was generated in code. The concepts behind signatures, the classes that take part and the workflows a WPF application builds from them are summarized below. A first signed document is created in [Digitally Sign a PDF](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/getting-started/pdf/sign/llms-full.txt) in Getting Started, from a button in *MainWindow.xaml*. ### What a Signature Proves and What It Doesn't A digital signature gives the recipient of a PDF two guarantees: - **Integrity.** A change to the document after signing makes the signature invalid, and PDF readers report it. - **Authenticity.** The certificate of the signature identifies the signer. Recipients trust it when it was issued by a certificate authority (CA) they trust. Self-signed certificates are for tests and internal documents. Two things are outside what a signature proves: - **The time of signing.** Without a time server, the date and time come from the clock of the signing computer. A trusted timestamp is the subject of [Timestamp Configuration](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/timestamps/llms-full.txt). - **Confidentiality.** A signed document can be read by anyone who has the file. Passwords and permissions protect the content, as [Passwords and Access Permissions](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/pdf/passwords/llms-full.txt) describes, and a document can have both. [Protections of TX Text Control](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/security/overview/#protections-of-tx-text-control) in Security compares what each mechanism protects against. ### Electronic Signatures and Digital Signatures - **An electronic signature** is a visible mark: a scanned handwritten signature, a typed name, a stamp. In a TX Text Control document, it's the image shown in a signature field. It isn't secured cryptographically by itself. - **A digital signature** binds the document to the signer's certificate and is secured cryptographically. TX Text Control creates it while it saves the PDF. Most signing processes combine both: a signature field shows the image of a handwritten signature, and a certificate signs that field. A digital signature of the whole document, on the other hand, has no visible representation on the pages. ### Two Ways to Sign Signatures are created only when a document is saved as PDF or PDF/A. For all other formats, the signature settings have no meaning. - **The whole document** gets one invisible signature, the usual choice when an organization certifies a generated invoice or report. See [Signing PDF Documents](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/signing/llms-full.txt). - **Signature fields** get one signature each, with the image the field shows. Several people can sign one document this way. See [Signature Fields and Signature Appearance](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/signature-fields/llms-full.txt) and [Multiple Signatures](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/multiple/llms-full.txt). Signing PDF and PDF/A documents was introduced in version 17.0, and signature fields in version 31.0. The fields are saved with the TX Text Control format, DOCX and RTF too, so a document can travel between signers in an editable format; only the save as PDF applies the certificates. Adobe Acrobat Reader lists the signatures of a document in its **Signatures** panel, including the field of each signature. A whole-document signature appears as an invisible signature: ![Adobe Acrobat with the Signatures panel open, listing a valid signature whose field is an invisible signature.](https://docs.textcontrol.com/assets/img/tx-text-control-dotnet-wpf/signature-panel-invisible.62a2f499.webp) ### The Classes and Controls Involved | Part | Role | Described in | |---|---|---| | [DigitalSignature](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol/digitalsignature/llms-full.txt) | Holds the certificate, the URL of a time server and, for a signature field, the name of the field | [Certificates](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/certificates/llms-full.txt) | | [SaveSettings.DigitalSignature](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol/savesettings/digitalsignature-property/llms-full.txt) | Signs the whole document when it's saved | [Signing PDF Documents](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/signing/llms-full.txt) | | [SaveSettings.SignatureFields](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol/savesettings/signaturefields-property/llms-full.txt) | Signs named signature fields, one `DigitalSignature` per field | [Signature Fields and Signature Appearance](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/signature-fields/llms-full.txt) | | [SignatureField](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol/signaturefield/llms-full.txt), [SignatureImage](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol/signatureimage/llms-full.txt), [SignerData](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol/signerdata/llms-full.txt) | A field in the document, its image and the data of the suggested signer | [Signature Fields and Signature Appearance](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/signature-fields/llms-full.txt) | | [WPF.TextControl.SignatureFields](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-wpf/textcontrol/signaturefields-property/llms-full.txt) | The signature fields of the document in the editor | [Signature Fields](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/document-editor/signature-fields/llms-full.txt) in Document Editor | | [RibbonInsertTab](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-wpf/ribboninserttab/llms-full.txt), [RibbonFrameLayoutTab](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol-wpf/ribbonframelayouttab/llms-full.txt) | Let users insert signature fields and enter the signer data on the ribbon | [Signature Fields](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/document-editor/signature-fields/llms-full.txt) in Document Editor | | [ServerTextControl](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/reference/txtextcontrol/servertextcontrol/llms-full.txt) | Creates, merges and signs documents in code, without a window | [Signing PDF Documents](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/signing/#sign-a-merged-document-in-the-background) | The signature classes are in the `TXTextControl` namespace and are the same in all .NET products of TX Text Control; only the editor, `TXTextControl.WPF.TextControl`, and its ribbon are WPF classes. `DigitalSignature` takes a .NET `X509Certificate2` with its private key, from a *.pfx* file or the Windows certificate store, as [Certificates](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/certificates/llms-full.txt) describes. ### Signing on the User's Computer A WPF application signs on the computer it runs on. The certificate with its private key therefore has to be available there: - **Personal certificates** are installed in the user's Windows certificate store, possibly on a smart card or USB token, and the user picks one when signing. The private key stays on the user's computer. - **An organization's certificate** that certifies generated documents must be protected on every computer that signs with it, and never shipped with the application, as [Certificate and Private Key Handling](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/security/certificates/llms-full.txt) describes. For a trusted timestamp, the computer needs a connection to the time server while it saves. Only a hash of the signature is sent there, not the document. ### Typical Workflows - **Sign what the user wrote.** The user edits a document in the window, and a button saves it as a signed PDF, to a fixed path or through the **Save As** dialog box. - **Generate and sign.** A `ServerTextControl` merges a DOCX template with data and saves a signed PDF/A document, while the editor stays untouched. - **Collect signatures, then certify.** A document with one named field per signer travels from person to person in the TX Text Control format, and the last step signs all fields at once. - **Archive for the long term.** Documents signed with a CA certificate and a trusted timestamp are archived unchanged. ### Next Steps - [Signing PDF Documents](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/signing/llms-full.txt): sign the document of the editor or a generated one. - [Certificates](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/certificates/llms-full.txt): load certificates and let users choose theirs. - [Signature Fields and Signature Appearance](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/signature-fields/llms-full.txt): sign visible signature fields. - [Timestamp Configuration](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/timestamps/llms-full.txt): add a trusted signing time. --- ## Nearby - **Previous:** [Digital Signatures](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/llms-full.txt) - **Next:** [Signing PDF Documents](https://docs.textcontrol.com/tx-text-control-dotnet-wpf/digital-signatures/signing/llms-full.txt)