HtmlToPdf

A high-performance, native PDF rendering engine for .NET — no browser engine required.

Get Started  ·  Features  ·  API Reference

Overview

HtmlToPdf converts HTML documents — complete with CSS styling, images, and LaTeX math — directly into multi-page PDF files. Unlike tools that rely on headless browsers (Puppeteer, Playwright, wkhtmltopdf), this project uses a custom-built layout engine powered by SkiaSharp to render PDFs natively in C#.

This means:

• Zero browser dependencies — no Chromium downloads, no headless processes, no sandbox issues.
• Low resource footprint — runs efficiently without spawning external processes.
• Full control — every stage of the pipeline (parsing, layout, rendering) is written in C# and fully customizable.

Features

Core Rendering

• Custom Layout Engine — A purpose-built layout engine (~1800 lines) that handles block/inline flow, page breaks, margin collapsing, and element positioning across multiple pages.
• CSS Support — Parses <style> blocks and inline styles. Supports fonts, colors, backgrounds, borders, margins, padding, text alignment, and more.
• Table Rendering — Full HTML table support with borders, cell padding, header styling, colspan, and adaptive column width calculation.
• Image Support — Inline base64-encoded images (data:image/png;base64,...) rendered directly into the PDF.
• Lists — Ordered (<ol>) and unordered (<ul>) list rendering with proper bullet/number prefixes.
• Horizontal Rules — <hr> elements rendered as styled dividers.

Math & Science

• LaTeX Math — Inline ($...$) and display ($$...$$) math expressions rendered using CSharpMath. Supports fractions, integrals, matrices, Greek letters, summations, and more.
• Math Pre-measurement — LaTeX expressions are parsed and measured before layout, ensuring accurate positioning alongside text content.

Text & Internationalization

• Unicode Support — Full Unicode text rendering with HarfBuzz text shaping for complex scripts.
• Bengali Script — Native support for Bengali and other Indic scripts that require advanced shaping.
• Font Caching — Intelligent font resolution and caching system for fast repeated renders.

Conversion Modes

• HTML String — Paste or programmatically send raw HTML.
• File Upload — Upload .html, .htm, or .xhtml files.
• URL Fetching — Provide a URL and the engine fetches and converts the page.
• Batch Processing — Upload multiple HTML files at once. Files are converted in parallel across all available CPU cores and returned as a ZIP archive.

Page Configuration

• Page Sizes — A3, A4, A5, Letter, Legal
• Orientation — Portrait or Landscape
• Margins — Configurable margin in millimeters

Tech Stack

Component	Library	Purpose
Web Framework	ASP.NET Core 8	HTTP server, MVC routing, file handling
HTML Parsing	AngleSharp	Standards-compliant HTML/CSS DOM parser
PDF Rendering	SkiaSharp	2D graphics engine with native PDF document backend
Text Shaping	SkiaSharp.HarfBuzz	Complex script shaping (Bengali, Arabic, Devanagari, etc.)
Math Rendering	CSharpMath.SkiaSharp	LaTeX math typesetting

Getting Started

Prerequisites

• .NET 8 SDK or later

Installation

# Clone the repository
git clone https://github.com/Naieem-55/Html-to-Pdf.git
cd Html-to-Pdf

# Restore dependencies
dotnet restore

# Run the application
dotnet run

The application will start and display the URL in the console (typically https://localhost:5001).

Quick Start

1. Open the web UI in your browser.

2. Choose an input method:

   Tab	Description
   HTML Editor	Write or paste HTML directly into the editor
   File Upload	Upload a .html / .htm / .xhtml file
   URL	Enter a webpage URL to fetch and convert

3. Adjust page settings (size, orientation, margins) as needed.

4. Click Convert to PDF to generate and download your file.

For bulk operations, switch to the Batch Convert tab, upload multiple files, and receive a ZIP archive of all converted PDFs.

Architecture

Project Structure

HtmlToPdf/
├── Controllers/
│   ├── HomeController.cs            # Landing page
│   └── PdfController.cs             # Single + batch conversion endpoints
├── Services/
│   ├── FreeHtmlToPdfConverter.cs     # Core rendering pipeline (layout engine + PDF renderer)
│   ├── StyleSheetParser.cs          # CSS rule parsing and cascade resolution
│   ├── FontCache.cs                 # System font discovery and caching
│   └── MathCache.cs                 # LaTeX expression pre-measurement and render cache
├── Models/
│   └── ConvertViewModel.cs          # View models and DTOs
├── Views/
│   ├── Pdf/
│   │   ├── Index.cshtml             # Converter UI (tabs, editor, settings)
│   │   └── _PdfSettings.cshtml      # Shared page settings partial
│   ├── Home/Index.cshtml            # Home page
│   └── Shared/                      # Layout and error views
├── wwwroot/                         # Static assets (CSS, JS, favicon)
└── Program.cs                       # Application entry point and DI configuration

Rendering Pipeline

The conversion follows a five-stage pipeline:

HTML Input
    │
    ▼
┌─────────────────────────────────────────────────────────────┐
│  1. PARSE        │  HTML → DOM tree (AngleSharp)            │
├──────────────────┼──────────────────────────────────────────┤
│  2. STYLE        │  CSS rules + inline styles → resolved    │
│                  │  properties per element                  │
├──────────────────┼──────────────────────────────────────────┤
│  3. MATH         │  Detect $...$ and $$...$$ expressions,   │
│                  │  pre-measure dimensions (CSharpMath)     │
├──────────────────┼──────────────────────────────────────────┤
│  4. LAYOUT       │  Block/inline flow → positioned boxes    │
│                  │  with automatic page breaks              │
├──────────────────┼──────────────────────────────────────────┤
│  5. RENDER       │  Paint boxes to multi-page PDF           │
│                  │  (SkiaSharp PDF backend)                 │
└──────────────────┴──────────────────────────────────────────┘
    │
    ▼
PDF Output

API Reference

POST /Pdf/Convert

Converts a single HTML source to a PDF file.

Content-Type: multipart/form-data

Parameter	Type	Default	Description
ConversionSource	string	"html"	Input mode: "html", "file", or "url"
HtmlContent	string	—	Raw HTML content (when source is "html")
HtmlFile	file	—	HTML file upload (when source is "file")
Url	string	—	Webpage URL (when source is "url")
PageSize	string	"A4"	Page size: A3, A4, A5, Letter, Legal
Landscape	bool	false	Enable landscape orientation
MarginMm	int	10	Page margin in millimeters

Response: application/pdf — the generated PDF file.

Max request size: 50 MB

---

POST /Pdf/BatchConvert

Converts multiple HTML files in parallel and returns them as a ZIP archive.

Content-Type: multipart/form-data

Parameter	Type	Description
HtmlFiles	file[]	Multiple HTML files to convert
PageSize	string	Page size (same options as above)
Landscape	bool	Enable landscape orientation
MarginMm	int	Page margin in millimeters

Response: application/zip — ZIP archive containing all converted PDFs.

Max request size: 200 MB

Supported HTML Elements

Element	Support
Headings (h1–h6)	Full
Paragraphs (p, div, span)	Full
Text formatting (b, strong, i, em, u)	Full
Links (a)	Styled (rendered as text)
Tables (table, tr, td, th, colspan)	Full
Lists (ol, ul, li)	Full
Images (img with base64 src)	Full
Horizontal rules (hr)	Full
Line breaks (br)	Full
Blockquotes (blockquote)	Full
Inline math ($...$)	Full
Display math ($$...$$)	Full

Example

<!DOCTYPE html>
<html>
<head>
    <style>
        body { font-family: Arial, sans-serif; margin: 40px; color: #333; }
        h1 { color: #2c3e50; border-bottom: 2px solid #3498db; padding-bottom: 10px; }
        table { width: 100%; border-collapse: collapse; margin: 20px 0; }
        th, td { border: 1px solid #bdc3c7; padding: 10px; text-align: left; }
        th { background: #3498db; color: white; }
    </style>
</head>
<body>
    <h1>Sample Document</h1>
    <p>The quadratic formula is $x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$</p>

    <p>$$\int_{-\infty}^{\infty} e^{-x^2} dx = \sqrt{\pi}$$</p>

    <table>
        <tr><th>Feature</th><th>Status</th></tr>
        <tr><td>CSS Styling</td><td>Supported</td></tr>
        <tr><td>LaTeX Math</td><td>Supported</td></tr>
        <tr><td>Tables</td><td>Supported</td></tr>
    </table>
</body>
</html>

Contributing

Contributions are welcome. Please open an issue to discuss proposed changes before submitting a pull request.

License

This project is open source. See the repository for license details.