LeafSide

A fast, native PDF reader for Windows that scrolls like butter, on ARM64 and x64.

Highlight, take notes, search and print — without lag, without ads, without an account.

⬇️ Download the latest version

Built with WinUI 3 and PDFium, it runs as native code on Windows on Arm (Surface and other Snapdragon laptops and tablets) as well as on Intel and AMD PCs. Scrolling never waits for a page to render, and pages stay sharp at any zoom.

✨ Features

🚀 Smooth by design Continuous scrolling with inertia, at 60 fps or more Pinch, touchpad and Ctrl+wheel zoom from 10 % to 1000 % Sharp text at any zoom, rendered in the background Native ARM64 build: no x64 emulation	🖍️ Highlights and notes Highlighter in four colors, sticky notes and comments Saved inside the PDF as standard annotations: Edge, Acrobat and phone apps show them too A Notes panel lists them all; click one to jump to it Undo / redo, and a prompt before closing with unsaved changes
📑 Find your way Tabs, page thumbnails and the table of contents Search with every match highlighted Internal and web links, with Back / Forward Select text with mouse or pen and copy it	🔖 Picks up where you left off Remembers the page, the exact position and the zoom of every file Reopens the tabs of your last session Recent files on the start page
🌙 Comfortable reading Night mode with inverted colors Full screen (F11) Double-tap zoom on touch screens English and Spanish UI, following Windows	🖨️ Fits into Windows Printing through the Windows dialog, as sharp vector output Open with for PDFs; files open as tabs in the same window Drag and drop, password-protected PDFs Installer or portable zip, no admin rights needed

Every highlight and note in one panel	Night mode and the table of contents

🔒 Private by design: no account, no telemetry, no ads. Your files never leave your PC.

⬇️ Download

Get the latest version from Releases:

Device	Installer (recommended)	Portable zip
Intel / AMD PCs	LeafSide-<version>-win-x64.msi	LeafSide-<version>-win-x64.zip
Windows on Arm (Surface with Snapdragon, other ARM64 PCs)	LeafSide-<version>-win-arm64.msi	LeafSide-<version>-win-arm64.zip

• Installer: double-click the .msi. It installs for your user only (no administrator rights) into %LocalAppData%\Programs\LeafSide, adds a Start menu entry and Open with for PDFs, updates older versions in place, and is removed from Settings → Apps.
• Zip: extract the whole zip and run LeafSide.exe.

Neither needs the .NET runtime. The app isn't code-signed yet, so SmartScreen may ask you to confirm: click More info → Run anyway.

Requires Windows 10 version 2004 (build 19041) or later; Windows 11 recommended.

⌨️ Keyboard shortcuts

Keys	Action
Ctrl+O / Ctrl+W	Open file / close tab
Ctrl+F, F3 / Shift+F3	Search, next / previous match
Ctrl+G	Go to page
Ctrl+ / Ctrl- / Ctrl+0	Zoom in / out / fit width
Alt+← / Alt+→ (or mouse back/forward buttons)	Back / forward
Ctrl+P	Print
Ctrl+S / Ctrl+Shift+S	Save highlights and notes / save as
Ctrl+Z / Ctrl+Y	Undo / redo (highlights and notes)
F11, Esc	Full screen, exit full screen
Space / PgUp / PgDn / Home / End	Scroll by screen, go to first / last page

How it stays smooth

Many PDF readers stutter on ARM devices for two reasons: they run emulated (x64 code translated to ARM64), and they render pages on the same thread that handles scrolling. This reader avoids both:

1. The compositor scrolls, not the UI thread. WinUI's ScrollView (InteractionTracker) moves the content at display refresh rate even while the app is busy.
2. Only pages near the viewport exist. Page elements are virtualized and recycled.
3. Rendering happens in the background, most urgent first. A dedicated render thread uses a priority queue. Visible pages come before prefetch, and pages that scroll out of view are cancelled before they're rendered.
4. Progressive quality. Each page first shows a cheap thumbnail, then a sharp bitmap for the current zoom. Above ~8 megapixels it switches to 1024 px tiles, and only the visible ones are rendered. During a pinch the existing bitmaps are scaled, and they are re-rendered once the zoom settles.
5. GPU upload off the UI thread. Bitmaps become CompositionDrawingSurfaces (Win2D) on the render thread, so the UI thread only attaches finished surfaces.
6. Native PDFium for x64 and ARM64 via P/Invoke.

Measured with the built-in benchmark (a 300-page document with dense vector art, continuous scrolling, x64 release build):

Zoom	Frame p50	Frame p99	Frames over 33 ms
125 % (whole-page bitmaps)	5.5 ms	9.6 ms	0
300 % (tiles)	5.6 ms	8.6 ms	0

Run it yourself: drag a PDF onto Benchmark.bat in the release folder, or run LeafSide.exe --bench file.pdf. The result is written to %LocalAppData%\PdfReader\bench.log.

Building from source

Requirements: Windows 10/11 and the .NET 10 SDK. Visual Studio is optional; everything builds with the dotnet CLI. The Windows App SDK, Win2D and PDFium come from NuGet or are included in the repository.

dotnet test tests/PdfReader.Core.Tests                      # unit tests
dotnet build src/PdfReader.App -c Release -p:Platform=x64   # or -p:Platform=ARM64
.\build\publish.ps1                                         # zips and MSI installers for both, in artifacts\

To run a debug build: src\PdfReader.App\bin\x64\Debug\net10.0-windows10.0.22621.0\win-x64\LeafSide.exe [file.pdf].

tests/assets/make_sample.py (Python 3) generates the heavy 300-page sample.pdf used for manual and benchmark testing.

Project layout

src/PdfReader.Core     UI-independent engine: PDFium P/Invoke, page layout, render scheduler, LRU cache,
                       tile planner, search, annotations (undo, saving), reading state, navigation history,
                       print layout
src/PdfReader.App      WinUI 3 app: PdfViewer (virtualized pages), PageView, DocumentView, MainWindow,
                       services (state, printing, file association, localization)
src/native/pdfium      pdfium.dll for win-x64 and win-arm64 (with licenses)
tests/                 xUnit tests for Core, engine and localization resources
installer/             Per-user MSI (WiX Toolset 5, restored from NuGet)
packaging/             Files shipped next to the exe (README.txt, LEEME.txt, Benchmark.bat)
build/publish.ps1      Release packaging

Localization

UI strings live in src/PdfReader.App/Strings/<language>/Resources.resw. en-US is the default and es is Spanish. XAML uses x:Uid, and code uses Loc.Get / Loc.Format. To add a language, copy the en-US folder and translate it. LocalizationTests checks that every language has the same keys and placeholders. Set PDFREADER_LANGUAGE=en-US (or es) to force a language when testing.

Data and privacy

The only network request is the update check: once a day, LeafSide asks GitHub's public API for the latest release (api.github.com/repos/Jmzp/leafside/releases/latest). It sends nothing about you or your files, only the app's name and version as the User-Agent. Downloads start only when you click the button, and the file's SHA-256 is checked against the one GitHub publishes. Turn the check off with Check for updates automatically on the start page.

The app only writes to a PDF when you save your highlights and notes, and then the save is incremental and atomic: the original bytes are kept, and a failed save never leaves a damaged file. It stores:

• its state (reading positions, recent files, open tabs, settings) in %LocalAppData%\PdfReader\state.json;
• the Open with registration under HKCU\Software\Classes (LeafSide.exe --unregister removes it).

Limitations

• Annotations are limited to highlights and notes (other kinds are shown but not edited). No form filling or page editing. Encrypted PDFs can be read but not annotated.
• The print dialog shows no preview.
• Releases are not code-signed yet.

License

LeafSide is free software, licensed under the GNU General Public License v3.0 or later: you can use, study, share and modify it, and versions you distribute must stay open under the same license. Version 1.0.0 was released under the MIT license. Third-party components and their licenses are listed in THIRD-PARTY-NOTICES.md.