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APIs
+ Digital Signature
+
+
Organize Pages
- Overview
diff --git a/Document-Processing/PDF/PDF-Viewer/angular/digital-signature/add-digital-signature.md b/Document-Processing/PDF/PDF-Viewer/angular/digital-signature/add-digital-signature.md
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+---
+layout: post
+title: Add Digital Signature to PDF in Angular PDF Viewer | Syncfusion
+description: Learn how to add signature fields and apply PKI-based digital signatures using Syncfusion Angular PDF Viewer and JavaScript PDF Library.
+platform: document-processing
+control: PdfViewer
+documentation: ug
+---
+
+# Add Digital Signature to PDF in Angular
+
+This section explains how to **add signature fields** using the Syncfusion **Angular PDF Viewer** and how to apply **digital (PKI) signatures** using the **JavaScript PDF Library**.
+
+N> As instructed by team leads — use the **Angular PDF Viewer only to add & place signature fields**. Use the **JavaScript PDF Library** to apply the *actual cryptographic digital signature*.
+
+## Overview (Explanation)
+
+A **digital signature** provides:
+- **Authenticity** – confirms the signer’s identity.
+- **Integrity** – detects modification after signing.
+- **Non‑repudiation** – signer cannot deny signing.
+
+Syncfusion supports a hybrid workflow:
+- Viewer → **[Design signature fields](../forms/manage-form-fields/create-form-fields#signature-field)**, capture Draw/Type/Upload electronic signature.
+- PDF Library → **[Apply PKCS#7/CMS digital signature](https://help.syncfusion.com/document-processing/pdf/pdf-library/javascript/digitalsignature)** using a certificate (PFX/P12).
+
+## Add a Signature Field (How-to)
+
+### Using the UI
+1. Open **Form Designer**.
+2. Select **Signature Field**.
+3. Click on the document to place the field.
+4. Configure Name, Tooltip, Required, etc.
+
+
+
+### Using the API
+{% tabs %}
+{% highlight ts tabtitle="Standalone" %}
+ this.pdfviewer.formDesignerModule.addFormField('SignatureField', {
+ name: 'ApproverSignature',
+ pageNumber: 1,
+ bounds: { X: 72, Y: 640, Width: 220, Height: 48 },
+ isRequired: true,
+ tooltip: 'Sign here'
+ }as any);
+{% endhighlight %}
+{% endtabs %}
+
+## Capture Electronic Signature (Draw / Type / Upload)
+Users click the field → dialog appears → they can **Draw**, **Type**, or **Upload** a handwritten signature.
+
+This creates a *visual* signature only (not cryptographically secure).
+
+## Apply PKI Digital Signature (JavaScript PDF Library)
+
+Digital signature must be applied using **@syncfusion/ej2-pdf**.
+
+```ts
+import { PdfDocument, PdfSignature, PdfSignatureField, CryptographicStandard, DigestAlgorithm } from '@syncfusion/ej2-pdf';
+
+const document = new PdfDocument(pdfBytes);
+const page = document.getPage(0);
+
+let field = new PdfSignatureField(page, 'ApproverSignature', {
+ x: 72,
+ y: 640,
+ width: 220,
+ height: 48
+});
+document.form.add(field);
+
+const signature = PdfSignature.create(
+ {
+ cryptographicStandard: CryptographicStandard.cms,
+ digestAlgorithm: DigestAlgorithm.sha256
+ },
+ pfxBytes,
+ password
+);
+
+field.setSignature(signature);
+const signedBytes = await document.save();
+document.destroy();
+```
+
+N> See the PDF Library [Digital signature](https://help.syncfusion.com/document-processing/pdf/pdf-library/javascript/digitalsignature) to know more about Digital Signature in PDF Documents.
+
+## Important Notes
+- **Do all form edits first. Sign last.** Any PDF modification *after signing* invalidates the signature.
+- Self‑signed PFX will show **Unknown / Untrusted** until added to Trusted Certificates.
+
+## Best Practices
+- Place signature fields via Viewer for accurate layout.
+- Apply PKI signature using PDF Library only.
+- Use CMS + SHA‑256 for compatibility.
+- Avoid flattening after signing.
+
+## See Also
+- [Validate Digital Signatures](./validate-digital-signatures)
+- [Custom fonts for Signature fields](../../how-to/custom-font-signature-field)
+- [Signature workflows](./signature-workflow)
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diff --git a/Document-Processing/PDF/PDF-Viewer/angular/digital-signature/customize-signature-appearance.md b/Document-Processing/PDF/PDF-Viewer/angular/digital-signature/customize-signature-appearance.md
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+---
+layout: post
+title: Customize Signature Appearance in Angular PDF Viewer | Syncfusion
+description: Learn here all about how to customize visible PKI digital signature appearances using the Syncfusion PDF Library in Angular PDF Viewer.
+platform: document-processing
+control: PdfViewer
+documentation: ug
+---
+
+# Customize Signature Appearance in Angular
+
+This page explains how to customize the visual appearance of PKI [digital signature](https://help.syncfusion.com/document-processing/pdf/pdf-library/javascript/digitalsignature) (visible signature appearance) produced with the Syncfusion PDF Library.
+
+## Overview
+
+When applying a PKI [digital signature](https://help.syncfusion.com/document-processing/pdf/pdf-library/javascript/digitalsignature) you can create a visible appearance that includes text, images (logo/seal), fonts, and layout. Appearance rendering is done by composing signature appearance graphics with the PDF Library and embedding that appearance into the signature field.
+
+For implementation details and exact API usage, check the Syncfusion PDF Library references:
+
+- .NET PDF Library — [Drawing text/image in the signature appearance]( https://help.syncfusion.com/document-processing/pdf/pdf-library/net/working-with-digitalsignature#drawing-textimage-in-the-signature-appearance)
+- JavaScript PDF Library — [Drawing text/image in the signature appearance](https://help.syncfusion.com/document-processing/pdf/pdf-library/javascript/digitalsignature#drawing-textimage-in-the-signature-appearance)
+
+## What you can customize
+
+- Text (signer name, signing reason, date, descriptive labels)
+- Fonts, sizes, and styles
+- Images (company logo, seal, signature image)
+- Layout and bounding box for the visible appearance
+- Visible vs invisible signatures
+
+## Guidance
+
+- Use the [PDF Library](https://help.syncfusion.com/document-processing/pdf/pdf-library/javascript/digitalsignature) APIs to draw strings and images into the signature appearance graphics; attach the resulting appearance to the signature field before finalizing the PKI signature.
+- Prefer embedding high‑quality logo/seal images and use readable fonts for accessibility.
+- Keep the appearance compact to avoid overlapping form content and to preserve signature validation data.
+- Test appearances across typical page sizes and DPI settings to ensure consistent rendering.
+
+## Best Practices
+
+- Use consistent branding for signature visuals.
+- Keep appearance elements minimal and readable.
+- Avoid including data that might change after signing (dates shown should reflect signing time provided by the TSA when used).
+- When producing legally binding signatures, ensure the PKI signing process and appearance comply with your legal/operational requirements.
+
+## See Also
+
+- [Add Digital Signature](./add-digital-signature)
+- [Validate Digital Signatures](./validate-digital-signatures)
+- [Custom fonts for Signature fields](../../how-to/custom-font-signature-field)
+- [Signature workflows](./signature-workflow)
diff --git a/Document-Processing/PDF/PDF-Viewer/angular/digital-signature/signature-workflow.md b/Document-Processing/PDF/PDF-Viewer/angular/digital-signature/signature-workflow.md
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+---
+layout: post
+title: Digital Signature Workflows in Angular PDF Viewer | Syncfusion
+description: Learn how to add signature fields and apply digital (PKI) signatures in the Syncfusion Angular PDF Viewer.
+platform: document-processing
+control: PdfViewer
+documentation: ug
+---
+
+# Digital Signature Workflows in Angular
+
+This guide shows how to design signature fields, collect handwritten/typed e‑signatures in the browser, and apply **digital certificate (PKI) signatures** to PDF forms using the Syncfusion Angular PDF Viewer and the JavaScript PDF Library. Digital signatures provide **authenticity** and **tamper detection**, making them suitable for legally binding scenarios.
+
+## Overview
+
+A **digital signature** is a cryptographic proof attached to a PDF that verifies the signer's identity and flags any post‑sign changes. It differs from a simple electronic signature (handwritten image/typed name) by providing **tamper‑evidence** and compliance with standards like CMS/PKCS#7. The Syncfusion **JavaScript PDF Library** exposes APIs to create and validate digital signatures programmatically, while the **Angular PDF Viewer** lets you design signature fields and capture handwritten/typed signatures in the browser.
+
+## Quick Start
+
+Follow these steps to add a **visible digital signature** to an existing PDF and finalize it.
+
+1. **Render the Angular PDF Viewer with form services**
+
+{% tabs %}
+{% highlight ts tabtitle="Standalone" %}
+import { Component, ViewChild } from '@angular/core';
+import {
+ PdfViewerComponent,
+ PdfViewerModule,
+ ToolbarService,
+ MagnificationService,
+ NavigationService,
+ LinkAnnotationService,
+ BookmarkViewService,
+ ThumbnailViewService,
+ PrintService,
+ TextSelectionService,
+ TextSearchService,
+ AnnotationService,
+ FormFieldsService,
+ FormDesignerService,
+ PageOrganizerService
+} from '@syncfusion/ej2-angular-pdfviewer';
+
+@Component({
+ selector: 'app-root',
+ standalone: true,
+ template: `
+
+
+
+
+ `,
+ imports: [PdfViewerModule],
+ providers: [
+ ToolbarService,
+ MagnificationService,
+ NavigationService,
+ LinkAnnotationService,
+ BookmarkViewService,
+ ThumbnailViewService,
+ PrintService,
+ TextSelectionService,
+ TextSearchService,
+ AnnotationService,
+ FormFieldsService,
+ FormDesignerService,
+ PageOrganizerService
+ ]
+})
+export class AppComponent {
+
+ @ViewChild('pdfViewer')
+ public pdfViewer!: PdfViewerComponent;
+
+ public document: string =
+ 'https://cdn.syncfusion.com/content/pdf/form-filling-document.pdf';
+
+ public resource: string =
+ 'https://cdn.syncfusion.com/ej2/31.2.2/dist/ej2-pdfviewer-lib';
+}
+{% endhighlight %}
+{% endtabs %}
+
+The Viewer requires **FormFields** and **FormDesigner** services for form interaction and design, and `resourceUrl` for proper asset loading in modern setups.
+
+2. **Place a signature field (UI or API)**
+ - **UI:** Open **Form Designer** → choose **Signature Field** → click to place → configure properties like required, tooltip, and thickness.
+ 
+ - **API:** Use `addFormField('SignatureField', options)` to create a signature field programmatically.
+
+{% tabs %}
+{% highlight ts tabtitle="Standalone" %}
+import { Component, ViewChild } from '@angular/core';
+import {
+ PdfViewerComponent,
+ PdfViewerModule,
+ ToolbarService,
+ MagnificationService,
+ NavigationService,
+ LinkAnnotationService,
+ BookmarkViewService,
+ ThumbnailViewService,
+ PrintService,
+ TextSelectionService,
+ TextSearchService,
+ AnnotationService,
+ FormFieldsService,
+ FormDesignerService,
+ PageOrganizerService
+} from '@syncfusion/ej2-angular-pdfviewer';
+
+@Component({
+ selector: 'app-root',
+ standalone: true,
+ template: `
+
+
+
+
+ `,
+ imports: [PdfViewerModule],
+ providers: [
+ ToolbarService,
+ MagnificationService,
+ NavigationService,
+ LinkAnnotationService,
+ BookmarkViewService,
+ ThumbnailViewService,
+ PrintService,
+ TextSelectionService,
+ TextSearchService,
+ AnnotationService,
+ FormFieldsService,
+ FormDesignerService,
+ PageOrganizerService
+ ]
+})
+export class AppComponent {
+
+ @ViewChild('pdfViewer')
+ public pdfViewer!: PdfViewerComponent;
+
+ public document: string =
+ 'https://cdn.syncfusion.com/content/pdf/form-filling-document.pdf';
+
+ public resource: string =
+ 'https://cdn.syncfusion.com/ej2/31.2.2/dist/ej2-pdfviewer-lib';
+
+ onDocumentLoad(): void {
+ (this.pdfViewer as any).formDesignerModule.addFormField('SignatureField', {
+ name: 'ApproverSignature',
+ pageNumber: 1,
+ bounds: { X: 72, Y: 640, Width: 220, Height: 48 },
+ isRequired: true,
+ tooltip: 'Sign here'
+ });
+ }
+}
+{% endhighlight %}
+{% endtabs %}
+
+3. **Apply a PKI digital signature (JavaScript PDF Library)**
+
+The library provides `PdfSignatureField` and `PdfSignature.create(...)` for PKI signing with algorithms such as **SHA‑256**.
+
+```ts
+import {
+ PdfDocument, PdfSignatureField, PdfSignature,
+ CryptographicStandard, DigestAlgorithm
+} from '@syncfusion/ej2-pdf';
+
+// Load existing PDF bytes (base64/ArrayBuffer)
+const document = new PdfDocument(data);
+const page = document.getPage(0);
+
+// Create a visible signature field if needed
+const field = new PdfSignatureField(page, 'ApproverSignature', {
+ x: 72, y: 640, width: 220, height: 48
+});
+
+// Create a CMS signature using a PFX (certificate + private key)
+const signature = PdfSignature.create(
+ { cryptographicStandard: CryptographicStandard.cms, digestAlgorithm: DigestAlgorithm.sha256 },
+ certData,
+ password
+);
+
+field.setSignature(signature);
+document.form.add(field);
+
+const signedBytes = await document.save('signed.pdf');
+document.destroy();
+```
+
+N> For sequential or multi‑user flows and digital signature appearances, see these live demos: [eSigning PDF Form](https://document.syncfusion.com/demos/pdf-viewer/angular/#/bootstrap5/pdfviewer/esigning-pdf-forms), [Invisible Signature](https://document.syncfusion.com/demos/pdf-viewer/angular/#/bootstrap5/pdfviewer/invisible-digital-signature) and [Visible Signature](https://document.syncfusion.com/demos/pdf-viewer/angular/#/bootstrap5/pdfviewer/visible-digital-signature) in the Angular Sample Browser.
+
+## How‑to guides
+
+### Add a signature field (UI)
+Use the Form Designer toolbar to place a **Signature Field** where signing is required. Configure indicator text, required state, and tooltip in the properties pane.
+
+ 
+
+### Add a signature field (API)
+
+Adds a signature field programmatically at the given bounds.
+
+{% tabs %}
+{% highlight ts tabtitle="Standalone" %}
+{% raw %}
+(this.pdfViewer as any).formDesignerModule.addFormField('SignatureField', {
+ name: 'CustomerSign',
+ pageNumber: 1,
+ bounds: { X: 56, Y: 700, Width: 200, Height: 44 },
+ isRequired: true
+});
+{% endraw %}
+{% endhighlight %}
+{% endtabs %}
+
+### Capture handwritten/typed signature in the browser
+
+When users click a signature field at runtime, the Viewer’s dialog lets them **draw**, **type**, or **upload** a handwritten signature image—no plugin required—making it ideal for quick approvals.
+
+ 
+
+N> For a ready‑to‑try flow that routes two users to sign their own fields and then finalize, open [eSigning PDF Form](https://document.syncfusion.com/demos/pdf-viewer/angular/#/bootstrap5/pdfviewer/esigning-pdf-forms) in the sample browser.
+
+### Apply a PKI digital signature
+
+Use the **JavaScript PDF Library** to apply a cryptographic signature on a field, with or without a visible appearance. See the **Digital Signature** documentation for additional options (external signing callbacks, digest algorithms, etc.).
+
+N> To preview visual differences, check the [Invisible Signature](https://document.syncfusion.com/demos/pdf-viewer/angular/#/bootstrap5/pdfviewer/invisible-digital-signature) and [Visible Signature](https://document.syncfusion.com/demos/pdf-viewer/angular/#/bootstrap5/pdfviewer/visible-digital-signature) in our Sample Browser. Digital Signature samples in the Angular sample browser.
+
+### Finalize a signed document (lock)
+
+After collecting all signatures and passing validations, **[Lock](https://help.syncfusion.com/document-processing/pdf/pdf-library/javascript/digitalsignature#lock-signature)** the PDF (and optionally restrict permissions) to prevent further edits.
+
+## Signature Workflow Best Practices (Explanation)
+
+Designing a well‑structured signature workflow ensures clarity, security, and efficiency when working with PDF documents. Signature workflows typically involve multiple participants—reviewers and approvers each interacting with the document at different stages.
+
+### Why structured signature workflows matter
+
+A clear signature workflow prevents improper edits, guarantees document authenticity, and reduces bottlenecks during review cycles. When multiple stakeholders sign or comment on a document, maintaining order is crucial for compliance, traceability, and preventing accidental overwrites.
+
+### Choosing the appropriate signature type
+
+Different business scenarios require different signature types. Consider the purpose, regulatory requirements, and level of trust demanded by the workflow.
+
+- **Handwritten/typed (electronic) signature** – Best for informal approvals, acknowledgments, and internal flows. (Captured via the Viewer’s signature dialog.)
+
+ 
+
+- **Digital certificate signature (PKI)** – Required for legally binding contracts and tamper detection with a verifiable signer identity. (Created with the JavaScript PDF Library.)
+
+N> You can explore and try out live demos for [Invisible Signature](https://document.syncfusion.com/demos/pdf-viewer/angular/#/bootstrap5/pdfviewer/invisible-digital-signature) and [Visible Signature](https://document.syncfusion.com/demos/pdf-viewer/angular/#/bootstrap5/pdfviewer/visible-digital-signature) in our Sample Browser.
+
+### Pre‑signing validation checklist
+
+To prevent rework, validate the PDF before enabling signatures:
+- Confirm all **required form fields** are completed (names, dates, totals). (See [Form Validation](../forms/form-validation).)
+- Re‑validate key values (financial totals, tax calculations, contract amounts).
+- Lock or restrict editing during review to prevent unauthorized changes.
+- Use [annotations](../annotation/overview) and [comments](../annotation/comments) for clarifications before signing.
+
+### Role‑based authorization flow
+
+- **Reviewer** – Reviews the document and adds [comments/markups](../annotation/comments). Avoid placing signatures until issues are resolved.
+ 
+- **Approver** – Ensures feedback is addressed and signs when finalized.
+ 
+- **Final Approver** – Verifies requirements, then [Lock Signature](https://help.syncfusion.com/document-processing/pdf/pdf-library/javascript/digitalsignature#lock-signature) to make signatures permanent and may restrict further edits.
+
+N> **Implementation tip:** Use the PDF Library’s `flatten` when saving to make annotations and form fields permanent before the last signature.
+
+### Multi‑signer patterns and iterative approvals
+- Route the document through a defined **sequence of signers**.
+- Use [comments and replies](../annotation/comments#add-comments-and-replies) for feedback without altering document content.
+- For external participants, share only annotation data (XFDF/JSON) when appropriate instead of the full PDF.
+- After all signatures, **[Lock](https://help.syncfusion.com/document-processing/pdf/pdf-library/javascript/digitalsignature#lock-signature)** to lock the file.
+
+N> Refer to [eSigning PDF Forms](https://document.syncfusion.com/demos/pdf-viewer/angular/#/bootstrap5/pdfviewer/esigning-pdf-forms) sample that shows two signers filling only their designated fields and finalizing the document.
+
+### Security, deployment, and audit considerations
+
+- **Restrict access:** Enforce authentication and role‑based permissions.
+- **Secure endpoints:** Protect PDF endpoints with token‑based access and authorization checks.
+- **Audit and traceability:** Log signature placements, edits, and finalization events for compliance and audits.
+- **Data protection:** Avoid storing sensitive PDFs on client devices; prefer secure server storage and transmission.
+- **Finalize:** After collecting all signatures, lock to prevent edits.
+
+## See also
+- [Create and Modify Annotation](../annotation/create-modify-annotation)
+- [Customize Annotation](../annotation/customize-annotation)
+- [Digital Signature - JavaScript PDF Library](https://help.syncfusion.com/document-processing/pdf/pdf-library/javascript/digitalsignature)
+- [Handwritten Signature](../annotation/signature-annotation)
+- [Form Fields API](../form-fields-api)
+- [Add Digital Signature](./add-digital-signature)
+- [Customize Signature Appearance](./customize-signature-appearance)
+- [Signature workflows](./signature-workflow)
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diff --git a/Document-Processing/PDF/PDF-Viewer/angular/digital-signature/validate-digital-signatures.md b/Document-Processing/PDF/PDF-Viewer/angular/digital-signature/validate-digital-signatures.md
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+---
+layout: post
+title: Validate Digital Signatures in Angular PDF Viewer | Syncfusion
+description: Learn how to validate digital signatures applied to PDF forms using the Syncfusion JavaScript PDF Library with the Angular PDF Viewer.
+platform: document-processing
+control: PdfViewer
+documentation: ug
+---
+
+# Validate Digital Signatures in Angular
+
+This guide explains **how to validate digital signatures** on PDFs when using the **Syncfusion Angular PDF Viewer** together with the **JavaScript PDF Library**. It clarifies what the Viewer does (display fields and signature appearances) and what the **PDF Library** does (perform **cryptographic validation** and produce validation results).
+
+N> **Important:** The Angular PDF Viewer renders signature fields and their visual appearances, but **cryptographic validation is performed by the JavaScript PDF Library**. Use the library to check integrity, certificate trust, and timestamp status, and surface the result in your UI.
+
+## Overview (Explanation)
+
+A **digital signature** is a cryptographic proof embedded in the PDF that allows verifiers to confirm:
+
+- **Document integrity** – The PDF has not changed since it was signed.
+- **Signer identity & trust** – The signer’s certificate chains to a trusted authority or is trusted locally.
+- **Timestamp validity** – (If present) the signature was time‑stamped by a trusted TSA at signing time.
+- **Revocation status** – Whether the signer’s certificate was revoked at or after signing (OCSP/CRL).
+
+ In Syncfusion, you typically **[design the signature field in the Viewer](../forms/manage-form-fields/create-form-fields#signature-field)** and then use the Syncfusion PDF Library to perform cryptographic validation. See the PDF Library documentation for API references and examples: [Digital signature validation (PDF Library)](https://help.syncfusion.com/document-processing/pdf/pdf-library/net/working-with-digitalsignature#digital-signature-validation).
+
+## How validation fits in the Viewer flow (Concept)
+
+1. Load and interact with the PDF in **Angular PDF Viewer** (place fields, fill forms).
+2. Use **JavaScript PDF Library** to **open the PDF bytes** and **validate the signature**.
+3. Display the validation outcome (valid/invalid/unknown) in your Angular UI (badge, toast, side panel).
+
+ ## How‑to: Validate a digital signature (Client‑side)
+
+ Cryptographic signature validation is performed by the Syncfusion PDF Library. Please refer to the PDF Library documentation for detailed guidance and sample code. The following pages cover validation concepts, APIs, and full examples:
+
+- [Digital signature validation overview](https://help.syncfusion.com/document-processing/pdf/pdf-library/net/working-with-digitalsignature#digital-signature-validation)
+
+- [Validate all signatures in a PDF document](https://help.syncfusion.com/document-processing/pdf/pdf-library/net/working-with-digitalsignature#validate-all-signatures-in-pdf-document)
+
+- [Validate and classify digital signatures in a PDF document](https://help.syncfusion.com/document-processing/pdf/pdf-library/net/working-with-digitalsignature#validate-and-classify-digital-signatures-in-a-pdf-document)
+
+After using the PDF Library to obtain validation results (integrity, trust, timestamp), surface those results in your Angular UI (for example: badge, table, or details panel) to communicate status to users.
+
+## Interpreting validation outcomes (Reference)
+
+- **Valid** – Integrity OK **and** certificate is trusted. (Timestamp valid if present.)
+- **Invalid** – Bytes changed after signing **or** signature object malformed.
+- **Unknown/Not Trusted** – Integrity OK but signer certificate is not trusted locally (common with **self‑signed PFX** used for demos). Import the signer certificate into the trusted store to see a *Valid* badge.
+
+## Best practices (Explanation)
+
+- **Single‑save rule:** Do **all edits first**, then **sign**, and **do not modify** the PDF after signing; modifying bytes after signing will invalidate the signature.
+- **Establish trust:** For demos, a self‑signed PFX will appear *Unknown*. For production, use a certificate that chains to a trusted CA or import the signer/issuer to the verifier’s trust store.
+- **Prefer timestamp (TSA):** A trusted timestamp improves long‑term validation even if the signer’s cert later expires or is revoked.
+- **Surface status in UI:** Show a clear badge (Valid/Invalid/Unknown) near the signature field or toolbar, and offer a *View details* panel with integrity, trust, and timestamp info.
+
+## Troubleshooting
+
+- **Signature shows Invalid** – Check whether the PDF was modified **after** signing (e.g., second save/flatten). Re‑sign as the last step.
+- **Unknown signer** – You are using a **self‑signed** PFX. Import the certificate into the validator’s trust store or use a CA‑issued certificate.
+- **Algorithm unsupported** – Use CMS/PKCS#7 with SHA‑256 (avoid SHA‑1).
+- **No revocation info** – Ensure OCSP/CRL endpoints are reachable by the validator or embed revocation data if supported.
+
+## See also
+- [Add Digital Signature](./add-digital-signature)
+- [Customize Signature Appearance](./customize-signature-appearance)
+- [Signature workflows](./signature-workflow)
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