Windows never had a PDF reader that is fast and lightweight and modern-looking at the same time. SumatraPDF is legendary for speed but wears a 2009 UI; Edge and Acrobat are heavy; Okular's Windows port doesn't feel native. Rune combines:

• the speed of SumatraPDF / Zathura — instant open, smooth scrolling through 1,000-page documents, strict memory budget
• the look and feel of GNOME Papers — a slim single header bar, a floating zoom control, a big-thumbnail sidebar — rebuilt natively on Windows 11 (Mica, dark mode, tabs in the title bar)
• a keyboard-first workflow — command palette, full arrow/vim navigation, a shortcuts overlay (F1), every action reachable without the mouse

Dark	Night mode (inverted pages)

Features

• Tabs in the title bar (Chrome-style), lazy-loaded — background tabs cost nothing until shown
• Continuous virtualized scrolling with tile-based progressive rendering (blurry-fast → crisp), rock-steady even while searching and scrolling a 1,000-page document at once
• Zoom 10–640% at the cursor from a floating zoom pill, fit-width / fit-page, rotation
• Sidebar (open by default, F9) with a switcher for thumbnails / chapters / bookmarks; internal & web links; back/forward history
• Full keyboard navigation — arrows scroll and page, PageUp/PageDown, Home/End (plus optional vim keys)
• Text selection & copy, find-in-document with highlight-all and hit stepping
• Form filling: click a field and type — text boxes, dropdowns and checkboxes, saved back into the PDF. Standard AcroForm documents only; XFA forms (some tax and government PDFs) say so plainly instead of silently ignoring your typing, and form JavaScript doesn't run, so auto-calculating fields won't recalculate
• Flatten: bake annotations and filled fields into the page so they can't be edited back out
• Signature details: for a digitally signed PDF, shows the signer's stated reason, time and format, and whether the signature covers the whole file. Rune does not verify signatures — it has no cryptography and never claims a signature is valid
• Annotation toolbar: pen, highlighter, note, sign and eraser sit together in the middle of the header; picking one opens its colours, size and opacity right beneath it. The highlighter works in a single gesture — just drag across the text — and still writes real PDF markup, so highlights stay attached to the words and other readers understand them
• Sign a document: draw your signature with the mouse or pen, or import a picture of one, then click to place it (drag if you want a specific size). Saved signatures are reusable and stay on your machine. This is a visible signature — ink on the page, like signing a printout — not a cryptographic one
• Annotations: highlight, underline, strikeout, sticky notes, and freehand pen/ink — saved as standard PDF annotations any reader can see (Ctrl+H highlight, Ctrl+E pen, Esc to put the tool away, right-click menu, Ctrl+S / Ctrl+Shift+S)
• Page editing in the thumbnail sidebar: multi-select, drag to reorder, Delete, copy/cut/paste pages (Ctrl+C/X/V, works across open tabs), or drop a PDF onto the sidebar to insert its pages
• Undo / redo for annotations and page edits (Ctrl+Z / Ctrl+Y)
• Bookmarks (Ctrl+B): name a page and jump back later; saved per document
• Presentation mode (F5): fullscreen, one page at a time, arrows / space / click to advance
• Keyboard shortcuts overlay (F1)
• Night mode: GPU-inverted page colors for dark-room reading (Ctrl+I)
• Recent-documents homepage: a clean grid of first-page thumbnails of your last files
• Command palette (Ctrl+K) with fuzzy filtering and go-to-page
• Session restore: reopens your tabs at the exact scroll position
• Pinch-to-zoom (touch/touchpad) and Ctrl+scroll, zoom at the cursor
• Self-updating: checks GitHub for new releases and updates in place (portable build; toggle in Settings)
• Printing with live preview and page ranges
• Opens damaged PDFs gracefully; 4 GB-file streaming without loading into memory

The interface follows GNOME Papers' proportions — one compact header row, with the rest tucked into a single menu — but is built entirely from native Windows 11 controls.

Keyboard shortcuts

Press F1 in the app for the full list. The essentials:

Action	Keys
Open / close tab	Ctrl+O / Ctrl+W
Scroll / screen up-down	↑ ↓ / PgUp PgDn, Space
Previous / next page	← / →
First / last page	Home / End
Find / next / previous	Ctrl+F / F3 / Shift+F3
Command palette / shortcuts	Ctrl+K / F1
Zoom in / out / 100% / fit page / fit width	Ctrl++ / Ctrl+- / Ctrl+1 / Ctrl+0 / Ctrl+2
Night mode / sidebar	Ctrl+I / F9
Rotate right / left	Ctrl+R / Ctrl+Shift+R
Presentation / bookmark page	F5 / Ctrl+B
Highlight / pen / save / save as	Ctrl+H / Ctrl+E / Ctrl+S / Ctrl+Shift+S
Copy / cut / paste (text or pages)	Ctrl+C / Ctrl+X / Ctrl+V
Undo / redo	Ctrl+Z / Ctrl+Y
Print / properties	Ctrl+P / Ctrl+D

Vim-style keys (j k h l, gg/G, p/n) can be enabled in Settings. Right-click a selection for underline/strikeout, or anywhere to add a note. Pen colour and width appear when you click the pen. In the thumbnail sidebar, Ctrl+C/X/V copy/cut/paste pages; elsewhere they act on selected text.

Install

Microsoft Store (recommended): one click, automatic updates, and it registers as a PDF handler — no certificate step, and nothing for SmartScreen to warn about.

Portable: grab rune-vX.Y.Z-win-x64.zip from Releases, extract anywhere, run Rune.exe. No installation, no registry. This is the build to use if you want Rune without the Store, or want to carry it on a USB stick.

Sideloaded MSIX: download the .msix and rune-signing.cer from Releases, then trust the certificate once (admin PowerShell):

Import-Certificate -FilePath rune-signing.cer -CertStoreLocation Cert:\LocalMachine\TrustedPeople
Add-AppxPackage -Path Rune.App_x.y.z.0_x64.msix

Smart App Control / SmartScreen apply to the GitHub downloads only — the Store build is signed by Microsoft. The portable and sideloaded builds are not yet code-signed, so machines with Smart App Control enabled will block them and SmartScreen may warn on first run ("More info → Run anyway").

The GitHub packages aren't size-optimized — they carry the full self-contained .NET + Windows App SDK runtimes.

Tech

Layer	Choice
UI	WinUI 3 (Windows App SDK 2.x), C# / .NET 10
PDF engine	PDFium (Chrome's renderer, BSD-3-Clause/Apache-2.0) via bblanchon/pdfium-binaries
Rendering	Win2D virtualized canvas ← LRU tile cache ← single render thread (PDFium is not thread-safe) ← thin P/Invoke

src/
  Rune.App/            WinUI 3 shell: tabs, viewer control, palette, print
  Rune.Engine/         document services, render scheduler, layout, search, state
  Rune.PdfiumInterop/  P/Invoke bindings over pdfium.dll
tests/
  Rune.Tests/          xUnit suite against a generated PDF corpus

Building

.NET 10 SDK on Windows — no Visual Studio required:

dotnet build src/Rune.App/Rune.App.csproj -p:Platform=x64
dotnet test tests/Rune.Tests/Rune.Tests.csproj

The debug build is an unpackaged self-contained exe — just run it.

Roadmap

Next: visible signature stamps (draw or import a signature and place it on the page), page extraction to a new file, more formats (ePub, CBZ), code signing for the GitHub builds, smaller packages.

Known limits: form JavaScript needs a V8-enabled PDFium build; text selection and annotation are disabled while the view is rotated; signature validation would need a cryptography stack Rune doesn't ship.

License

GPLv3 — free forever, and derivatives stay free. Built on PDFium (BSD-3-Clause/Apache-2.0), Win2D (MIT), the Windows App SDK, and .NET (MIT); see THIRD-PARTY-NOTICES.md.

A note on the Microsoft Store

Rune is published on the Microsoft Store as Rune PDF Reader, where it is covered by the Store's Standard Application License Terms. Those terms are generally considered incompatible with the GPL, so this deserves an explicit word:

Rune's own source is written entirely by its copyright holder, and its dependencies are permissively licensed (PDFium is BSD-3-Clause/Apache-2.0, Win2D and .NET are MIT) — there is no third-party copyleft code in it. As the sole copyright holder I can distribute my own work under whatever terms I choose, and I choose to make it available both under the GPLv3 here and through the Store for people who want automatic updates and one-click installation.

This does not change anything about the GPLv3 grant. The source in this repository is, and will remain, GPLv3: you may use, study, modify and redistribute it under those terms. The Store listing is an additional distribution channel, not a replacement, and every release is always available here as a portable download.