PDF Viewer Analysis

PDF Viewer Analysis

/app/pdf-viewer/ — Chrome Extension for PDF Rendering

Executive Summary

The pdf-viewer/ directory contains a Chrome extension implementing Mozilla's PDF.js library for in-browser PDF rendering. This extension is loaded by browser_guard.py to enable PDF viewing without external applications. The extension intercepts PDF URLs and renders them using HTML5 Canvas and JavaScript.

1. Directory Structure

pdf-viewer/
├── manifest.json              # Extension manifest (v3)
├── preferences_schema.json    # Settings schema
├── background.js              # Service worker
├── contentscript.js           # Content script injection
├── contentstyle.css           # Content script styles
├── extension-router.js        # URL routing logic
├── pdfHandler.js              # PDF handling logic
├── preserve-referer.js        # Referer preservation
├── suppress-update.js         # Update suppression
├── telemetry.js               # Usage analytics
├── icon16.png                 # Extension icons
├── icon48.png
├── icon128.png
├── options/                   # Options page
│   └── options.html
└── content/
    └── web/
        ├── cmaps/             # CJK character maps (~50 files)
        ├── images/            # UI icons
        ├── locale/            # Translations (~100 files)
        ├── standard_fonts/    # PDF standard Type 1 fonts (12 files)
        ├── viewer.html        # Main viewer HTML
        └── viewer.js          # PDF.js viewer implementation

2. Extension Identity

2.1 Manifest Analysis

{
  "minimum_chrome_version": "103",
  "manifest_version": 3,
  "name": "PDF Viewer",
  "version": "4.6.129",
  "description": "Uses HTML5 to display PDF files directly in the browser.",
  "permissions": [
    "alarms",
    "declarativeNetRequestWithHostAccess",
    "webRequest",
    "tabs",
    "webNavigation",
    "storage"
  ],
  "host_permissions": ["<all_urls>"],
  "content_scripts": [{
    "matches": ["http://*/*", "https://*/*", "file://*/*"],
    "run_at": "document_start",
    "all_frames": true,
    "css": ["contentstyle.css"],
    "js": ["contentscript.js"]
  }],
  "background": {
    "service_worker": "background.js"
  },
  "web_accessible_resources": [{
    "resources": ["content/web/viewer.html", "http:/*", "https:/*", ...],
    "matches": ["<all_urls>"],
    "extension_ids": ["*"]
  }]
}

2.2 Permissions Analysis

3. PDF Skill Integration

3.1 Connection to PDF Skill

PDF Skill (Creation/Processing)
    │
    ├── HTML Route ──► Playwright ──► Chromium
    │                                   │
    │                                   ├── PDF Viewer Extension
    │                                   │   └── Renders PDFs in browser
    │                                   │
    └── LaTeX Route ──► Tectonic ──► PDF output

3.2 How It Works

1. PDF Creation: PDF skill generates PDF via HTML+Paged.js or LaTeX+Tectonic
2. Browser Loading: browser_guard.py launches Chromium with --load-extension=/app/pdf-viewer
3. URL Interception: Extension intercepts PDF URLs via declarativeNetRequestWithHostAccess
4. Rendering: PDF.js renders PDF using HTML5 Canvas in viewer.html
5. Display: User views PDF directly in browser tab

3.3 No Direct Code Dependency

Important: The PDF Viewer extension and PDF skill are independent components:

Connection Point: Both use the browser, but don't share code directly.

4. Technical Implementation

4.1 PDF.js Core

viewer.js implements:

• PDF document parsing
• Page rendering (Canvas-based)
• Text layer extraction
• Annotation handling
• Search functionality
• Zoom/navigation controls

4.2 CMap Files (content/web/cmaps/)

Purpose: Character-to-glyph mapping for CJK fonts.

Count: ~50 .bcmap files

Examples:

• 78-EUC-H.bcmap — JIS X 0208 (1978), EUC encoding, horizontal
• GB-EUC-H.bcmap — GB 2312, EUC encoding, horizontal
• UniCNS-UTF8-H.bcmap — Unicode CNS (Taiwan), UTF-8, horizontal

4.3 Standard Fonts (content/web/standard_fonts/)

PDF Standard Type 1 Fonts:

• Courier (4 variants)
• Helvetica (4 variants)
• Times (4 variants)

Total: 12 OTF files

4.4 Localization (content/web/locale/)

Supported Languages: ~100

Examples: en, de, fr, es, zh-CN, zh-TW, ja, ko, ar, he, hi

5. Security Analysis

5.1 Extension Security

5.2 Content Security Policy

"content_security_policy": {
  "extension_pages": "script-src 'self' 'wasm-unsafe-eval'; object-src 'self'"
}

• wasm-unsafe-eval: Required for PDF.js WebAssembly optimizations
• No inline scripts allowed

5.3 Risk Mitigation

6. Browser Integration

6.1 Loading in browser_guard.py

args = [
    # ... other flags
    "--load-extension=/app/pdf-viewer",
    # ...
]

6.2 Runtime Behavior

1. Chrome starts with extension pre-loaded
2. Extension registers URL interception rules
3. When PDF URL detected, redirects to viewer.html
4. PDF.js fetches and renders PDF content

7. Inter-Module Relationships

pdf-viewer/
    ├── browser_guard.py (loads extension)
    │   └── Chromium (host browser)
    ├── PDF Skill (creates PDFs)
    │   └── Output PDF files
    └── User (views PDFs)

8. Code Metrics

Document Version: 1.0 Analysis Date: 2026-02-02