Feature/viewer annotation toggle (#4557)

# Description of Changes

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Please provide a summary of the changes, including:

- What was changed
- Why the change was made
- Any challenges encountered

Closes #(issue_number)
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---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

---------

Co-authored-by: Copilot <[email protected]>
Co-authored-by: James Brunton <[email protected]>

frontend/src/components/viewer/SignatureAPIBridge.tsx

@@ -3,6 +3,7 @@ import { useAnnotationCapability } from '@embedpdf/plugin-annotation/react';
 import { PdfAnnotationSubtype, PdfStandardFont, PdfTextAlignment, PdfVerticalAlignment, uuidV4 } from '@embedpdf/models';
 import { SignParameters } from '../../hooks/tools/sign/useSignParameters';
 import { useSignature } from '../../contexts/SignatureContext';
+import { useViewer } from '../../contexts/ViewerContext';
 
 export interface SignatureAPI {
   addImageSignature: (signatureData: string, x: number, y: number, width: number, height: number, pageIndex: number) => void;
@@ -20,11 +21,12 @@ export interface SignatureAPI {
 export const SignatureAPIBridge = forwardRef<SignatureAPI>(function SignatureAPIBridge(_, ref) {
   const { provides: annotationApi } = useAnnotationCapability();
   const { signatureConfig, storeImageData, isPlacementMode } = useSignature();
+  const { isAnnotationMode } = useViewer();
 
 
-  // Enable keyboard deletion of selected annotations - only when in signature placement mode
+  // Enable keyboard deletion of selected annotations - when in signature placement mode or viewer annotation mode
   useEffect(() => {
-    if (!annotationApi || !isPlacementMode) return;
+    if (!annotationApi || (!isPlacementMode && !isAnnotationMode)) return;
 
     const handleKeyDown = (event: KeyboardEvent) => {
       if (event.key === 'Delete' || event.key === 'Backspace') {
@@ -65,7 +67,7 @@ export const SignatureAPIBridge = forwardRef<SignatureAPI>(function SignatureAPI
 
     document.addEventListener('keydown', handleKeyDown);
     return () => document.removeEventListener('keydown', handleKeyDown);
-  }, [annotationApi, storeImageData, isPlacementMode]);
+  }, [annotationApi, storeImageData, isPlacementMode, isAnnotationMode]);
 
   useImperativeHandle(ref, () => ({
     addImageSignature: (signatureData: string, x: number, y: number, width: number, height: number, pageIndex: number) => {