## ADDED Requirements

### Requirement: Dual PDF Generation Modes

The system SHALL support two distinct PDF generation modes to serve different use cases for both OCR and Direct tracks.

#### Scenario: Download layout preservation PDF
- **WHEN** user requests PDF via `/api/v2/tasks/{task_id}/download/pdf`
- **THEN** PDF SHALL use layout preservation mode
- **AND** text positions SHALL match original document coordinates
- **AND** this option SHALL be available for both OCR and Direct tracks
- **AND** existing behavior SHALL remain unchanged

#### Scenario: Download reflow layout PDF without translation
- **WHEN** user requests PDF via `/api/v2/tasks/{task_id}/download/pdf?format=reflow`
- **THEN** PDF SHALL use reflow layout mode
- **AND** text SHALL flow naturally with consistent font sizes
- **AND** body text SHALL use approximately 12pt font size
- **AND** headings SHALL use larger font sizes (14-18pt)
- **AND** this option SHALL be available for both OCR and Direct tracks

#### Scenario: OCR track reading order in reflow mode
- **GIVEN** document processed via OCR track
- **WHEN** generating reflow PDF
- **THEN** system SHALL use explicit `reading_order` array from JSON
- **AND** elements SHALL appear in order specified by reading_order indices
- **AND** if reading_order is missing, fall back to spatial sort (y, x)

#### Scenario: Direct track reading order in reflow mode
- **GIVEN** document processed via Direct track
- **WHEN** generating reflow PDF
- **THEN** system SHALL use implicit element order from extraction
- **AND** elements SHALL appear in list iteration order
- **AND** PyMuPDF's sort=True ordering SHALL be trusted

---

### Requirement: Reflow PDF Semantic Structure

The reflow PDF generation SHALL preserve document semantic structure.

#### Scenario: Headings in reflow mode
- **WHEN** original document contains headings (title, h1, h2, etc.)
- **THEN** headings SHALL be rendered with larger font sizes
- **AND** headings SHALL be visually distinguished from body text
- **AND** heading hierarchy SHALL be preserved

#### Scenario: Tables in reflow mode
- **WHEN** original document contains tables
- **THEN** tables SHALL render with visible cell borders
- **AND** column widths SHALL auto-adjust to content
- **AND** table content SHALL be fully visible
- **AND** tables SHALL use appropriate cell padding

#### Scenario: Images in reflow mode
- **WHEN** original document contains images
- **THEN** images SHALL be embedded inline in flowing content
- **AND** images SHALL be scaled to fit page width if necessary
- **AND** images SHALL maintain aspect ratio

#### Scenario: Lists in reflow mode
- **WHEN** original document contains numbered or bulleted lists
- **THEN** lists SHALL preserve their formatting
- **AND** list items SHALL flow naturally

---

## MODIFIED Requirements

### Requirement: Translated PDF Export API

The system SHALL expose an API endpoint for downloading translated documents as PDF files using reflow layout mode only.

#### Scenario: Download translated PDF via API
- **GIVEN** a task with completed translation
- **WHEN** POST request to `/api/v2/translate/{task_id}/pdf?lang={lang}`
- **THEN** system returns PDF file with translated content
- **AND** PDF SHALL use reflow layout mode (not layout preservation)
- **AND** Content-Type is `application/pdf`
- **AND** Content-Disposition suggests filename like `{task_id}_translated_{lang}.pdf`

#### Scenario: Translated PDF uses reflow layout
- **WHEN** user downloads translated PDF
- **THEN** the PDF SHALL use reflow layout mode
- **AND** text SHALL flow naturally with consistent font sizes
- **AND** body text SHALL use approximately 12pt font size
- **AND** headings SHALL use larger font sizes (14-18pt)
- **AND** content SHALL be readable without magnification

#### Scenario: Translated PDF for OCR track
- **GIVEN** document processed via OCR track with translation
- **WHEN** generating translated PDF
- **THEN** reading order SHALL follow `reading_order` array
- **AND** translated text SHALL replace original in correct positions

#### Scenario: Translated PDF for Direct track
- **GIVEN** document processed via Direct track with translation
- **WHEN** generating translated PDF
- **THEN** reading order SHALL follow implicit element order
- **AND** translated text SHALL replace original in correct positions

#### Scenario: Invalid language parameter
- **GIVEN** a task with translation only to English
- **WHEN** user requests PDF with `lang=ja` (Japanese)
- **THEN** system returns 404 Not Found
- **AND** response includes available languages in error message

#### Scenario: Task not found
- **GIVEN** non-existent task_id
- **WHEN** user requests translated PDF
- **THEN** system returns 404 Not Found

---

### Requirement: Frontend Download Options

The frontend SHALL provide appropriate download options based on translation status.

#### Scenario: Download options without translation
- **GIVEN** a task without any completed translations
- **WHEN** user views TaskDetailPage
- **THEN** page SHALL display "Download Layout PDF" button (original coordinates)
- **AND** page SHALL display "Download Reflow PDF" button (flowing layout)
- **AND** both options SHALL be available in the download section

#### Scenario: Download options with translation
- **GIVEN** a task with completed translation
- **WHEN** user views TaskDetailPage
- **THEN** page SHALL display "Download Translated PDF" button for each language
- **AND** translated PDF button SHALL remain as single option (no Layout/Reflow choice)
- **AND** translated PDF SHALL automatically use reflow layout

#### Scenario: Remove outdated MADLAD-400 references
- **WHEN** displaying translation section
- **THEN** page SHALL NOT display "MADLAD-400" badge
- **AND** description text SHALL reflect cloud translation service (Dify)
- **AND** description SHALL NOT mention local model loading time
