[V2] feat(pdfa): add PDF/A-3b option with updated descriptions and translations (#5286)

# Description of Changes


This pull request adds support for the PDF/A-3b format in the PDF/A
conversion tool, updates the user interface to reflect this new option,
and enhances the translation strings to clarify the differences between
the PDF/A variants.

**PDF/A-3b support and UI update:**

* Added PDF/A-3b as an option in the PDF/A output format dropdown in
`ConvertToPdfaSettings.tsx`.
* Updated the PDF/A options note to mention that PDF/A-3b supports
embedded files, improving user guidance in both the UI and translation
strings.

**Localization improvements:**

* Added and updated relevant translation keys and values for PDF/A-3b
support and improved descriptions in both the TOML and JavaScript i18n
config files.


<img width="366" height="998" alt="image"
src="https://github.com/user-attachments/assets/c6db557a-2a9c-436d-bfb5-7360b33b0d36"
/>

Closes: #5173


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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

- [X] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [X] 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)
- [X] I have performed a self-review of my own code
- [X] 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)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### UI Changes (if applicable)

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

### Testing (if applicable)

- [X] 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.

Signed-off-by: Balázs Szücs <bszucs1209@gmail.com>

frontend/public/locales/en-GB/translation.toml

@@ -1249,7 +1249,7 @@ includeAllRecipients = "Include CC and BCC recipients in header"
 downloadHtml = "Download HTML intermediate file instead of PDF"
 pdfaOptions = "PDF/A Options"
 outputFormat = "Output Format"
-pdfaNote = "PDF/A-1b is more compatible, PDF/A-2b supports more features."
+pdfaNote = "PDF/A-1b is more compatible, PDF/A-2b supports more features, PDF/A-3b supports embedded files."
 pdfaDigitalSignatureWarning = "The PDF contains a digital signature. This will be removed in the next step."
 fileFormat = "File Format"
 wordDoc = "Word Document"

frontend/src/core/components/tools/convert/ConvertToPdfaSettings.tsx

@@ -22,7 +22,8 @@ const ConvertToPdfaSettings = ({
 
   const pdfaFormatOptions = [
     { value: 'pdfa-1', label: 'PDF/A-1b' },
-    { value: 'pdfa', label: 'PDF/A-2b' }
+    { value: 'pdfa', label: 'PDF/A-2b' },
+    { value: 'pdfa-3', label: 'PDF/A-3b' }
   ];
 
   return (
@@ -50,7 +51,7 @@ const ConvertToPdfaSettings = ({
           data-testid="pdfa-output-format-select"
         />
         <Text size="xs" c="dimmed">
-          {t("convert.pdfaNote", "PDF/A-1b is more compatible, PDF/A-2b supports more features.")}
+          {t("convert.pdfaNote", "PDF/A-1b is more compatible, PDF/A-2b supports more features, PDF/A-3b supports embedded files.")}
         </Text>
       </Stack>
     </Stack>

frontend/src/core/i18n/config.ts

@@ -28,6 +28,10 @@ i18n
           'convert.dpi': 'DPI',
           'convert.singleOrMultiple': 'Output',
           'convert.emailNote': 'Email attachments and embedded images will be included',
+           'convert.pdfaOptions': 'PDF/A Options',
+          'convert.outputFormat': 'Output Format',
+          'convert.pdfaNote': 'PDF/A-1b is more compatible, PDF/A-2b supports more features, PDF/A-3b supports embedded files.',
+          'convert.pdfaDigitalSignatureWarning': 'The PDF contains a digital signature. This will be removed in the next step.',
           'common.color': 'Color',
           'common.grayscale': 'Grayscale',
           'common.blackWhite': 'Black & White',