DocPreview — Lightweight Office & Document Previewer for Windows

DocPreview is an ultra-lightweight, elegant, read-only document previewer for Windows 10 & 11 built with C# (.NET 10) and WPF Fluent Design (Wpf.Ui).

It is designed strictly for instant previewing without the weight, memory consumption, or complexity of full office suites or Chromium/Electron apps.

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✨ Key Features

• ⚡ Ultra-Lightweight & Instant Startup:
  • ~8.6 MB published executable.
  • ~35–50 MB RAM footprint (reuses Windows Edge WebView2 runtime).
  • Sub-100ms document parse and rendering times.
• 🎨 Modern Windows 11 Fluent UI:
  • Authentic Mica translucent window backdrop.
  • System-synced Dark and Light modes.
  • Frameless title bar with system snap layouts and quick action buttons.
• 🧠 Smart Dual-Engine Architecture:
  • Engine A (Windows COM IPreviewHandler): Queries the Windows Registry for Microsoft Office preview handlers. If Office is installed, it leverages native COM with 100% fidelity and virtually zero memory overhead.
  • Engine B (High-Fidelity Standalone Engine): If Office is not installed on the system, the app seamlessly falls back to embedded, lightweight standalone parsers running 100% offline.
• 🖱️ Frictionless UX & Shell Integration:
  • Windows Explorer Right-Click Menu: Right-click any document in Windows Explorer and select "Preview with DocPreview".
  • Drag & Drop: Drop any file directly onto the window.
  • CLI & Shell Integration: Pass file path via arguments (DocViewer.exe "path\to\doc.xlsx").
  • Interactive Controls: Zoom in/out, sheet tabs for Excel, slide carousel for PowerPoint, live filter search for CSV, and "Open with App" shortcut.

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📁 Supported File Formats

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⌨️ Keyboard Shortcuts

🖱️ Windows Explorer Right-Click Integration

You can preview documents directly by right-clicking on them in Windows File Explorer:

1. Option A: One-Click Inside the App

   • Click the Add-Ins / Context Menu button (right side of toolbar) in the app to toggle it on or off.

2. Option B: Run the Included PowerShell Script

   • To enable: powershell -ExecutionPolicy Bypass -File .\register_context_menu.ps1
   • To remove: powershell -ExecutionPolicy Bypass -File .\unregister_context_menu.ps1

3. Option C: Command-Line Flags

   .\publish\DocViewer.exe --register
   .\publish\DocViewer.exe --unregister
   

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🚀 Running & Building

1. Run Development Build

dotnet run

2. Preview a Specific File via Command Line

dotnet run -- "test_samples\budget.xlsx"

3. Run Automated Self-Tests

Verifies document parsing and HTML generation for all supported formats:

dotnet run -- --test

4. Publish Single-File Release

dotnet publish -c Release -r win-x64 --self-contained false -p:PublishSingleFile=true -o publish

The resulting publish\DocViewer.exe is ~8.6 MB and ready for immediate deployment.

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📂 Project Structure

doc_viewer/
├── Assets/                        # Embedded webview scripts (docx-preview, jszip)
├── Controls/
│   └── PreviewHandlerHost.cs      # Win32 COM HwndHost for native Windows preview handlers
├── Services/
│   ├── DocumentPreviewService.cs  # Master routing & fallback engine
│   ├── RegistryHelper.cs          # Registry query for COM CLSIDs
│   ├── MarkdownRenderer.cs        # Markdig + GitHub dark/light styling
│   ├── CsvRenderer.cs             # Fast streaming CSV with search & sticky headers
│   ├── ExcelRenderer.cs           # Multi-sheet .xlsx & legacy .xls reader
│   ├── WordRenderer.cs            # Paginated .docx DOM renderer
│   └── PowerPointRenderer.cs      # Slide deck presentation viewer
├── test_samples/                  # Sample test documents (.docx, .xlsx, .pptx, .csv, .md)
├── MainWindow.xaml / .cs          # Fluent UI, Mica backdrop, Drag & Drop
├── App.xaml / .cs                 # Application startup, encoding, and self-test harness
└── DocViewer.csproj               # .NET 10 project definition