# SignatureField The `SignatureField` class corresponds to `FormFieldType.Signature` and stores digital signature data. Use it to sign PDF documents or validate existing signatures. > important To use the signing functionality in RadPdfProcessing for .NET Standard/.NET Core, you must add a reference to the `System.Security.Cryptography.Pkcs` NuGet package, version 9.0.9 or later. This functionality is available starting with R1 2022 SP1. ## Properties The `SignatureField` class provides the following properties: | Property | Description | | -------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `Signature` | Gets or sets the `Signature` value. Setting this property signs the document during export. Signing with multiple signatures is not supported. To validate a signature, use the `Validate()` and `TryValidate()` methods. Validation requires that the source stream is open and is performed against the document state at import time. See [Digital Signature](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/features/digital-signature/overview) for more details. | | `LockSettings` | Gets the `SignatureFieldLock` settings that control which form fields become read-only after this signature field is signed. Returns `null` when no lock settings exist. | | `Widgets` | The collection of Widget annotations representing the field on the PDF pages. Widgets can be added using `AddWidget()` and removed using `Remove()`. Implements `IEnumerable`. | **Create a SignatureField and Add It to a Page** ```C# RadFixedDocument document = new RadFixedDocument(); X509Certificate2 certificate = new X509Certificate2("JohnDoe.pfx", "johndoe"); SignatureField signatureField = new SignatureField("SampleSignature"); signatureField.Signature = new Signature(certificate); // The Signature property fo SignatureField is not available in PdfProcessing for .NET Standard. SignatureWidget widget = signatureField.Widgets.AddWidget(); widget.Rect = new Rect(200, 600, 100, 100); widget.Border = new AnnotationBorder(5, AnnotationBorderStyle.Solid, null); //Create a Form object to define the appearance you would like for the signature field. Telerik.Documents.Fixed.Model.Objects.Form form = new Telerik.Documents.Fixed.Model.Objects.Form(); form.FormSource = new FormSource(); form.FormSource.Size = new Size(120, 120); FixedContentEditor formEditor = new FixedContentEditor(form.FormSource); formEditor.DrawCircle(new Point(50, 50), 20); formEditor.DrawText("Sample Signature"); //Add the FormSource object to the widget of the field. widget.Content.NormalContentSource = form.FormSource; RadFixedPage page = document.Pages.Last(); page.Annotations.Add(widget); document.AcroForm.FormFields.Add(signatureField); ``` ## Locking Fields After Signing Before you sign, configure the lock on `SignatureField`, not `Signature.Settings`. Each method replaces the previous configuration with the corresponding `SignatureFieldLockAction`: | Method | Action | Result after signing | | ----------------------------------------------------- | --------- | ----------------------------------------------------------------------------------- | | `LockAllFields()` | `All` | Locks every form field in the document. | | `LockFields(IEnumerable fieldNames)` | `Include` | Locks only the named fields. An empty sequence locks no fields. | | `LockAllFieldsExcept(IEnumerable fieldNames)` | `Exclude` | Locks every form field except the named fields. An empty sequence locks all fields. | Use case-sensitive `FormField.Name` values. Both list-based methods copy the names, so later input changes have no effect. A `null` collection or field name throws `ArgumentNullException`. This example configures the approval signature to lock customer details and leave `ReviewerComment` unaffected: ```csharp Telerik.Documents.Fixed.Model.RadFixedDocument document = new Telerik.Documents.Fixed.Model.RadFixedDocument(); document.Pages.AddPage(); document.AcroForm.FormFields.AddTextBox("CustomerName"); document.AcroForm.FormFields.AddTextBox("CustomerEmail"); document.AcroForm.FormFields.AddTextBox("ReviewerComment"); Telerik.Documents.Fixed.Model.InteractiveForms.SignatureField signatureField = document.AcroForm.FormFields.AddSignature("Approval"); signatureField.LockFields(new[] { "CustomerName", "CustomerEmail" }); ``` Alternatively, use `signatureField.LockAllFields()` or `signatureField.LockAllFieldsExcept(new[] { "ReviewerComment" })`. To sign during export, assign a `Signature` and follow the [PDF signing workflow](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/features/digital-signature/getting-started). > important `LockAllFields()` also locks other signature fields. For a workflow with later signatures, exclude those signature fields or lock only the fields that must become read-only. ## Inspecting and Preserving Lock Settings Inspect `SignatureField.LockSettings` through `SignatureFieldLock.Action` and the read-only `Fields` list. Change the configuration only through the lock methods. **RadPdfProcessing** preserves signature-field lock settings when you import, export, or clone a document. An unsigned field can carry these settings for a later signature in RadPdfProcessing or another PDF application. When RadPdfProcessing signs the field, it writes a *FieldMDP transform*, a PDF signature rule that identifies the locked fields. It marks those fields as read-only in the output, not immediately in memory. Full-document export leaves source fields unchanged. Locks support certificate-based and external signatures with full-document export or [`PdfStreamSigner.SignDocument`](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/features/digital-signature/pdfstreamsigner). Use [`PdfStreamSigner.SignExistingField`](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/features/digital-signature/signing-existing-signature-fields) for lock settings already stored in the PDF. > important Preserved lock settings do not guarantee that existing signatures remain valid after a full import and export. Use incremental signing to preserve earlier signatures. ## See Also * [FormField](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/model/interactive-forms/form-fields/formfields) * [PDF Annotation Widgets](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/model/annotations/widgets) * [Digital Signature Workflows](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/features/digital-signature/overview) * [Incremental Signing of Existing Fields](https://www.telerik.com/document-processing-libraries/documentation/libraries/radpdfprocessing/features/digital-signature/signing-existing-signature-fields) * [Signature API Reference](https://docs.telerik.com/devtools/document-processing/api/Telerik.Windows.Documents.Fixed.Model.DigitalSignatures.Signature.html)