dxpdf — Fast DOCX to PDF Converter in Rust

Convert Microsoft Word DOCX files to PDF without Microsoft Office, LibreOffice, or any cloud API.

dxpdf is an open-source, standalone DOCX-to-PDF conversion engine written in Rust and powered by Skia. It reads .docx files and produces high-fidelity PDF output — preserving text formatting, tables, images, headers, footers, hyperlinks, and page layout. Available as a CLI tool, a Rust library, and a Python package.

Built by nerdy.pro.

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Key Features

• Blazing fast — converts multi-page documents in under 100 ms on modern hardware
• High fidelity — Flutter-inspired measure → layout → paint pipeline with pixel-accurate baseline positioning
• Type-safe — compile-time dimensional type system (Twips, Pt, Emu) prevents unit mixing bugs
• Standalone — no Office installation, no LibreOffice, no external services needed
• Cross-platform — runs natively on macOS, Linux, and Windows
• Three interfaces — use as a CLI tool, Rust library (use dxpdf;), or Python package (import dxpdf)
• ISO 29500 compliant — validated against the Office Open XML specification

Installation

Command-Line Tool

cargo install dxpdf

Rust Library

Add to your Cargo.toml:

[dependencies]
dxpdf = "0.2.25"

Python Package

pip install dxpdf

Usage

CLI — Convert DOCX to PDF from the Terminal

dxpdf input.docx                  # produces input.pdf
dxpdf input.docx -o output.pdf    # specify output path

Rust — Convert DOCX to PDF Programmatically

let docx_bytes = std::fs::read("document.docx")?;
let pdf_bytes = dxpdf::convert(&docx_bytes)?;
std::fs::write("output.pdf", &pdf_bytes)?;

You can also inspect or transform the parsed document model before conversion:

use dxpdf::{docx, model, render};

let document = docx::parse(&std::fs::read("document.docx")?)?;

for block in &document.blocks {
    match block {
        model::Block::Paragraph(p) => { /* inspect paragraph content */ }
        model::Block::Table(t) => { /* inspect table structure */ }
    }
}

let pdf_bytes = render::render(&document)?;

Python — Convert DOCX to PDF in Python

import dxpdf

# Bytes in, bytes out
pdf_bytes = dxpdf.convert(open("input.docx", "rb").read())

# File path to file path
dxpdf.convert_file("input.docx", "output.pdf")

Supported DOCX Features

dxpdf handles the most common DOCX features found in real-world business documents, reports, and forms:

Category	Features
Text formatting	Bold, italic, underline, highlighting, font size/family/color, character spacing, superscript/subscript, run shading
Paragraphs	Alignment (left/center/right), spacing (before/after/line with auto/exact/atLeast), indentation, tab stops, paragraph borders, paragraph shading
Tables	Column widths, cell margins (3-level cascade), merged cells (gridSpan + vMerge), row heights, borders, cell shading, nested tables
Images	Inline images (PNG, JPEG, BMP, WebP), floating/anchored images with alignment and percentage-based positioning
Styles	Paragraph and character styles, basedOn inheritance, document defaults, theme fonts
Headers & footers	Text, images, page numbers via PAGE/NUMPAGES field codes
Lists	Bullets, decimal, lower/upper letter, lower/upper roman numbering with counter tracking
Hyperlinks	Clickable PDF link annotations with URL resolution
Page layout	Multiple page sizes/margins, section breaks, portrait and landscape orientation
Pagination	Automatic page breaking, word wrapping, line spacing modes, floating image text flow

Performance Benchmarks

Benchmarked on Apple M3 Max with hyperfine (20 runs, 3 warmup):

Document type	Pages	Conversion time	Memory usage
Short form with tables and images	2	48 ms	20 MB
Multi-page report	7	52 ms	24 MB
Image-heavy document (60+ images)	24	353 ms	76 MB

dxpdf processes most business documents in under 100 ms, making it suitable for batch processing, server-side conversion, and CI/CD pipelines.

Building from Source

Prerequisites

• Rust toolchain (1.70+)

• clang (required by skia-safe for building Skia bindings)

• Linux only: libfontconfig1-dev and libfreetype-dev

  sudo apt-get install -y libfontconfig1-dev libfreetype-dev

Build

cargo build --release

The release binary will be at target/release/dxpdf.

Run Tests

cargo test

Architecture

dxpdf follows a measure → layout → paint pipeline inspired by Flutter's rendering model:

DOCX (ZIP) → Parse → Document Model → Measure → Layout → Paint → PDF
             Twips/Emu/HalfPoints       ←── Pt throughout ──→   Skia

Type-safe dimensions flow through the entire pipeline: OOXML units (Twips, Emu, HalfPoints) in the parsed model, Pt (typographic points) in layout, and f32 only at the Skia rendering boundary.

Each layout element (paragraphs, table cells, headers/footers) goes through three phases:

1. Measure — collect text fragments, fit lines, produce draw commands with relative coordinates
2. Layout — assign absolute positions, handle page breaks, distribute heights (e.g., vertically merged cells)
3. Paint — emit draw commands at final positions (shading → content → borders)

Module Overview

Module	Purpose
dimension	Type-safe dimensional units (Twips, HalfPoints, EighthPoints, Emu, Pt) with compile-time unit safety
geometry	Spatial types (Offset, Size, Rect, EdgeInsets, LineSegment) — generic over unit, with Skia interop
model	Algebraic data types representing the full document tree (Document, Block, Inline, etc.)
docx	DOCX ZIP extraction, declarative serde-based XML parser, style and numbering resolution
render/layout	Measure → layout → paint pipeline: fragment-based line fitting, paragraph layout, three-pass table layout, header/footer handling
render/painter	Skia canvas operations for PDF output
render/fonts	Font resolution with metric-compatible substitution (e.g., Calibri → Carlito, Cambria → Caladea)

OOXML Feature Coverage

Validated against ISO 29500 (Office Open XML). 37 features fully implemented, 9 partial, 13 planned.

Full feature matrix (click to expand)

Text Formatting (w:rPr)

Feature	Status
Bold, italic	✅ with toggle support
Underline	✅ font-proportional stroke width
Font size, family, color	✅
Superscript/subscript	✅
Character spacing	✅
Character scaling (w:w horizontal compression/expansion)	✅
Run shading	✅
Strikethrough	⚠️ parsed, not yet rendered
Highlighting	✅ full ST_HighlightColor palette
Caps, smallCaps	❌
Shadow, outline, emboss, imprint	❌
Hidden text	❌

Paragraph Properties (w:pPr)

Feature	Status
Alignment (left, center, right)	✅
Alignment (justify)	⚠️ parsed, renders left-aligned
Spacing before/after, line spacing	✅ auto/exact/atLeast
Indentation (left, right, first-line, hanging)	✅
Tab stops (left)	✅
Tab stops (center, right)	✅
Tab stops (decimal)	⚠️ rendered as left-aligned
Paragraph shading	✅
Paragraph borders	✅ with adjacent border merging, w:space offset
Keep with next, widow/orphan control	❌

Styles

Feature	Status
Paragraph styles, character styles	✅
basedOn inheritance	✅
Document defaults, theme fonts	✅

Tables

Feature	Status
Grid columns, cell widths (dxa)	✅
Cell widths (pct, auto)	⚠️ fall back to grid
Cell margins (3-level cascade)	✅
Merged cells (gridSpan, vMerge)	✅
Row heights	✅ min / ⚠️ exact treated as min
Table borders (per-cell, per-table)	✅
Border styles (single)	✅
Border styles (double, dashed, dotted)	⚠️ render as single
Cell shading (solid)	✅
Cell shading (patterns)	❌
Vertical alignment (top / center / bottom)	✅ incl. vMerge-aware bottom alignment
Row splitting across page breaks	✅ §17.4.1 cantSplit honored
Nested tables	✅

Images

Feature	Status
Inline images	✅ PNG, JPEG, BMP, WebP
Floating images	✅ offset, align, wp14:pctPos
Wrap modes	✅ none/square/tight/through
VML images	❌

Page Layout

Feature	Status
Page size and orientation	✅
Page margins (all 6)	✅
Section breaks (nextPage)	✅
Section breaks (continuous)	✅ continues on current page
Section breaks (even, odd)	⚠️ treated as nextPage
Multi-column, page borders, doc grid	❌

Headers & Footers

Feature	Status
Default header/footer	✅
First page, even/odd, per-section	❌

Lists

Feature	Status
Bullet, decimal, letter, roman	✅
Multi-level lists	⚠️ levels parsed, nesting limited

Fields

Feature	Status
PAGE, NUMPAGES	✅
Hyperlinks	✅ clickable PDF annotations
Unknown fields	✅ cached value fallback
TOC, MERGEFIELD, DATE	❌

Other

Feature	Status
Footnotes/endnotes	❌ warned
Comments, tracked changes	❌ / ⚠️
DrawingML shapes (preset geometry, fill, stroke, outer shadow)	⚠️ Tier 0-1 coverage
Text boxes, SmartArt, charts	❌
RTL text, automatic hyphenation	❌

Dependencies

Crate	Purpose
quick-xml	Declarative XML parsing via serde deserializers
zip	DOCX ZIP archive reading
skia-safe	PDF rendering, text measurement, link annotations
clap	CLI argument parsing
thiserror	Error types
log + env_logger	Logging for unsupported features (RUST_LOG=warn)
pyo3 (optional)	Python bindings via maturin

Frequently Asked Questions

How do I convert a DOCX file to PDF?

Install dxpdf with cargo install dxpdf, then run dxpdf input.docx. The PDF will be created in the same directory. You can also specify an output path with -o output.pdf.

Does dxpdf require Microsoft Office or LibreOffice?

No. dxpdf is a standalone converter that reads DOCX files directly and renders PDF output using Skia. No Office installation or external service is needed.

Can I use dxpdf as a library in my Rust or Python project?

Yes. In Rust, add dxpdf as a dependency and call dxpdf::convert(&docx_bytes). In Python, install with pip install dxpdf and call dxpdf.convert(bytes) or dxpdf.convert_file("input.docx", "output.pdf").

What DOCX features are supported?

dxpdf supports text formatting, paragraphs, tables (including nested and merged cells), inline and floating images, styles with inheritance, headers/footers, lists, hyperlinks, section breaks, and automatic pagination. See the full feature matrix above.

How fast is dxpdf?

On Apple M3 Max, dxpdf converts a typical multi-page business document in under 100 ms. A 24-page image-heavy document takes about 350 ms. It is designed for batch processing and server-side use.

What platforms does dxpdf support?

dxpdf runs on macOS, Linux, and Windows. On Linux, you need libfontconfig1-dev and libfreetype-dev installed.

Used By

• nerdy.pro
• formtastic.de

Contributing

Contributions are welcome. Please open an issue before submitting large PRs.

Built by nerdy.pro.

License

MIT