Hisui PDF

A cross-platform desktop PDF editor built on a fully free/MIT-licensed stack.

Hisui PDF lets you reorganise, annotate, redact and protect PDF documents from a single Avalonia desktop app that runs on Windows, Linux and macOS.

Download

Grab a ready-to-run build from the Releases page — the binaries are self-contained, so no .NET install is required.

Platform	Asset
Windows x64	Hisui.Pdf-vX.Y.Z-win-x64.zip
Linux x64	Hisui.Pdf-vX.Y.Z-linux-x64.tar.gz
macOS (Intel)	Hisui.Pdf-vX.Y.Z-osx-x64.tar.gz
macOS (Apple Silicon)	Hisui.Pdf-vX.Y.Z-osx-arm64.tar.gz

Unpack the archive and run Hisui.Pdf.App (.exe on Windows). On macOS the binary is unsigned, so on first launch right-click → Open (or run xattr -dr com.apple.quarantine Hisui.Pdf.App).

Features

• Pages — merge, split, extract, reorder, rotate and delete pages, with non-destructive editing and full undo/redo.
• Annotations — highlight, rectangle, free text, sticky notes, image overlays and document-wide watermarks (all undoable).
• Reusable signatures — build a library of signatures (draw freehand, import a PNG, or type cursive text) and reuse them across documents.
• Text editing — replace a word in place (redact-and-retype).
• Redaction — secure redaction that rasterises the page and removes the underlying text/vector content.
• Forms — read and fill AcroForm fields.
• Security & metadata — AES-256 encryption/decryption, document metadata editing.
• Extraction — pull out text (with coordinates) and embedded images.
• OCR — turn scanned (image-only) PDFs into searchable PDFs by adding an invisible, selectable text layer (Tesseract). Scanned pages are detected automatically.
• Localization — English and Italian UI, switchable at runtime.

Tech stack

• .NET 10 / C#
• Avalonia 11.2 — cross-platform UI
• PDFsharp — structural & write operations
• PdfPig — text/image extraction
• PDFtoImage (PDFium) — page rendering
• Tesseract — OCR for scanned PDFs
• SkiaSharp — raster compositing
• CommunityToolkit.Mvvm + Microsoft.Extensions.Hosting — MVVM & DI

Project structure

Project	Target	Role
src/Hisui.Pdf.Core	net10.0	PDF engine, no UI dependencies
src/Hisui.Pdf.App	net10.0	Avalonia desktop app (MVVM)
tests/Hisui.Pdf.Core.Tests	net10.0	xUnit v3 tests

Build & run

# Build
dotnet build Hisui.Pdf.slnx

# Run the app
dotnet run --project src/Hisui.Pdf.App

# Run the tests (xUnit v3 on Microsoft Testing Platform — run the test exe)
dotnet test Hisui.Pdf.slnx

OCR setup

OCR works out of the box. The English and Italian language data (eng/ita, the tessdata_fast models) ships in a tessdata folder next to the executable, and the native engine binaries are bundled on Windows via the Tesseract package.

• More languages — drop extra *.traineddata files into the tessdata folder next to the app (or point the TESSDATA_PREFIX environment variable at them) and pass the language code. Grab them from tessdata_fast.
• Native libraries on Linux/macOS — install the system Tesseract/Leptonica: on Linux libtesseract/libleptonica, on macOS brew install tesseract leptonica.

If a language or native library is missing the app reports a clear message instead of failing — the rest of the editor keeps working.

License

Hisui PDF is released under the MIT License.

It bundles third-party components under permissive licenses (MIT, Apache-2.0, BSD-3-Clause) and the Inter font (SIL OFL 1.1). See THIRD-PARTY-NOTICES.txt for the full attributions.