Folio

A fast, clean PDF reader for Windows, macOS, and Linux. Read, highlight, annotate, sign, and ask AI about your documents. Free and open source, with no Folio account required.

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All releases · Changelog · Prefer not to install on Windows? Folio-Portable.exe on the release page runs as-is (it doesn't auto-update).

Folio's builds aren't signed with paid developer certificates yet, so the first launch needs one extra step:

• Windows: if SmartScreen warns, choose More info → Run anyway.
• macOS: open the DMG and drag Folio to Applications. The first time you open it, macOS says it can't verify the developer: click Done, then go to System Settings → Privacy & Security and click Open Anyway.
• Linux (.deb): sudo apt install ./Folio-linux-amd64.deb, then open Folio from your applications menu. The package adds Folio's signed apt repository, so new versions arrive with your regular system updates (or sudo apt update && sudo apt upgrade). Copies installed from a .deb before 1.9 need the new .deb installed once.
• Linux (AppImage): make it executable (chmod +x Folio-linux-x86_64.AppImage) and run it. AppImages need FUSE 2: sudo apt install libfuse2t64 on Ubuntu 24.04 or later, libfuse2 on older releases.

Or build Folio yourself from source (below).

Features

Open PDFs and web links

• Local files: open a PDF with the file picker, drag and drop it anywhere in Folio, or use Open with → Folio from your file manager. The desktop app keeps one window, bringing an already-running copy forward when you open another PDF.
• PDF URLs: choose Open from URL (Ctrl+Shift+O), or drop a link or paste it with Ctrl+V outside a text field to fill it in, then press Open. Folio downloads and opens the PDF, follows redirects, and uses the server's filename when available. Folio asks once more before opening an address on your computer or local network.
• Webpage to PDF: use the same URL workflow for a webpage. Folio converts it into a PDF with selectable text, ready for highlights, notes, and Ask AI. The conversion preserves the site's on-screen layout, backgrounds, transparency, colors, and images instead of switching to its print styles.
• Word documents to PDF: open a .docx or .doc file the same ways as a PDF (Open with → Folio, the file picker, or drag and drop). Folio converts it, saves the PDF next to the original ("Report.docx" gets "Report.pdf"), and opens it. An existing PDF is never replaced; one that's newer than the document opens as is. Folio converts with Microsoft Word on Windows when it's installed, otherwise with LibreOffice, otherwise with its own converter for .docx (text, headings, lists, tables, and images, in a simpler layout). .doc files need Word or LibreOffice, except on macOS. Installing Folio adds it to Open with for Word documents without making it their default app.
• Password-protected PDFs: enter the password to read and annotate a protected document. These documents are not kept in the recent library, and their annotations and AI conversations are not persisted locally between sessions.
• Sample document: try the built-in tour from the home screen without finding a PDF first.

URL opening, webpage conversion, and Word conversion require the desktop app. Failed downloads leave your current document open.

Read and navigate

• Continuous scrolling with selectable text, previous/next controls, and a page-number field for jumping directly to a page.
• Pages and Outline tabs: browse page thumbnails or the PDF's existing outline/bookmarks; hide the sidebar when you want more reading space.
• Search as you type: match case or whole words, see the current match and total count, browse per-page snippets and match counts, and move between matches with Enter / Shift+Enter.
• Flexible views: fit to width, fit to page, automatic sizing, preset zoom levels, zoom buttons, Ctrl+wheel / trackpad pinch, two-page spreads, and page rotation.
• Focus mode: press F for distraction-free, fullscreen reading; press Esc to return.
• Light and dark themes, plus an independent Night reading setting that dims bright pages while keeping photos and figures in their original colors, including in thumbnails. Both settings survive restarts.

Highlight, draw, and take notes

• One-click highlights: select text, then choose yellow, green, blue, pink, or red from the selection toolbar; H applies the current highlight color.
• Notes on passages: type into the selection toolbar and press Enter to highlight with a note, or press N with text selected to focus the note box.
• Edit existing highlights: click one to recolor it, edit its note, ask AI about the passage, or remove it.
• Freehand drawing: choose Draw (D) and draw directly on the page in black, red, blue, green, or purple.
• Text boxes: choose Text (T) to add text to a page, using the same ink palette.
• Undo and redo annotation edits with the usual keyboard shortcuts; choose Done, V, or Esc to leave a drawing/text tool and return to selection.
• Notes tab: review highlights, their notes, and text boxes; click an entry to jump to it, edit a highlight's note, delete an entry, or ask AI about a highlight. A separate notes box holds thoughts about the whole document.
• Copy all as Markdown: copy document notes, highlighted passages, and text-box content with page references.
• Automatic local saving: highlights, notes, drawings, and text boxes return when you reopen an ordinary, non-password-protected PDF. Use Save a copy to share page annotations with other readers.

Add handwritten signatures

• Capture on paper: sign with dark ink on white paper, then use your camera or upload a PNG, JPEG, or WebP photo.
• Clean up the image: crop to the signature and adjust ink sensitivity to remove the paper background. Capture and image processing stay on your device.
• Suggested placement: Folio checks the current page for empty PDF signature fields and likely signature labels, then offers places to sign. Detection is a suggestion, not a guarantee that every field will be found.
• Preview and position: review the actual page, pick a suggestion or place the signature manually, and adjust its width before approving.
• Explicit approval: nothing is added until you click Approve and add signature. Signatures are visual stamps, not certificate-based digital signatures. Use Save a copy to keep a signed PDF; placed signatures are not part of Folio's automatic annotation restoration.
• Optional reuse: choose to remember a signature on this computer; remove the saved image in Settings → Signature → Forget.

Ask AI about a document

• Bring your own subscription: use Sign in with ChatGPT or your Claude subscription through Claude Code. No API key or separate Folio account is needed.
• Whole-document or passage questions: open the Ask AI panel from the toolbar, select text and choose Ask AI, or ask about an existing highlight.
• Streaming answers with clickable page citations that jump back to the source page.
• Rendered mathematics: inline and display LaTeX equations, with wide equations scrolling within the chat panel. Supports \( ... \), \[ ... \], $x$, and $$ ... $$; existing saved answers render too.
• Provider and model selection, a stop button for an in-progress answer, and a + button to start a fresh conversation.
• Per-document history: conversations are saved on this computer and restored when you reopen that document, except for password-protected PDFs. Starting a new conversation clears that document's saved chat.
• Account settings: choose your default provider, sign in to or out of ChatGPT, and check Claude Code's connection from Settings → Ask AI.

Ask AI is optional and desktop-only. See Using Ask AI for setup and Privacy for what is sent.

Inspect images

• Click a PDF image and choose View larger for a high-resolution, full-window view.
• Switch between Fit to window and Actual size, or copy the image to your clipboard.
• Choose Open in browser when an image has a web address. Images in converted webpages retain their original image links.

Pick up where you left off

• Recent library: keep up to eight recently opened PDFs with thumbnail previews and the last page read; reopen with one click, remove individual entries, or choose Clear all.
• Startup restore: reopen the last active document automatically when it is still in the recent library.
• Reading state: remember each document's page, scroll position, zoom, rotation, sidebar visibility, and two-page mode.
• Window state: restore the desktop window's size, monitor position, and maximized state.

Save, print, and inspect

• Save a copy (Ctrl+S) exports a PDF with page annotations, including highlights and attached notes, drawings, text boxes, and visual signatures. Your original file is not overwritten. Whole-document notes and AI chat history stay in Folio; copy notes as Markdown when you want to share them.
• Print (Ctrl+P) prints the current document with its page annotations.
• Document info shows available metadata: filename, title, author, subject, page count and size, file size, creation/modification dates, generating application, producer, and PDF version.

Settings and updates

Open ⋯ → Settings or press Ctrl+, for appearance, night reading, AI accounts and defaults, remembered signatures, and updates. About Folio shows the version, installed/portable edition, and installation location, with a shortcut to open that folder.

• Automatic updates on or off: the preference survives restarts. Turning it off stops background checks/downloads and automatic installation; manual Check for updates remains available for self-updating editions.
• Installed Windows: updates download in the background and install silently on exit, or when you choose Restart and update, without repeating the Setup wizard.
• Linux AppImage: downloads updates and replaces the AppImage. Linux .deb: updates through the signed apt repository and your system updater; Folio's toggle does not disable apt updates.
• macOS: current unsigned builds notify you and offer the download; self-installing updates require a signed build. Windows portable: download a replacement manually.
• Visible update status: checking, download progress, update-ready prompts, and errors are shown in the app.

Keyboard shortcuts

On macOS, use ⌘ wherever this table says Ctrl. Press ? with a document open for in-app help.

Current limits

• Folio annotates PDFs; it does not edit their original text/layout, merge or reorder pages, or provide OCR.
• Search, text selection, signature-label detection, and Ask AI depend on an existing PDF text layer. Image-only scans can still be viewed, drawn on, and signed, but do not gain searchable text automatically.
• Ask AI uses extracted text, not page images, and includes up to about 400,000 characters of document text. Long documents may be truncated; AI answers can be wrong, so check the cited pages.
• URL imports need a network connection and support public HTTP(S) links, with a 300 MB PDF download limit. Webpage conversion does not share your browser's cookies or sign-ins, so pages behind a login may not load as expected.
• Automatic local saving is not cloud sync or a replacement for exporting a PDF copy. Password-protected documents are not saved in Folio between sessions.

Using Ask AI

Open Ask AI with the sparkle button in the toolbar, or select text and choose Ask AI in the pop-up toolbar. Then pick a provider at the top of the panel:

• ChatGPT: click Continue with ChatGPT and sign in in your browser. Questions use your ChatGPT plan (Go, Plus, or Pro), and usage counts toward that plan's limits; manage it in ChatGPT settings. Sign out, or change the default provider, in Folio's Settings.
• Claude: install Claude Code, run claude once in a terminal, and sign in with your Claude account (Pro or Max). Then click Check again in Folio. Questions use your Claude subscription.

Ask AI is available in the desktop app only, not the browser version.

Privacy

Folio requires no Folio account, has no analytics or telemetry, and never uploads your documents on its own. It makes network requests only to:

• check GitHub for updates (installed copies; can be turned off in Settings),
• open a link you give it (a webpage is loaded in a hidden, sandboxed window with its own temporary session, so no cookies or sign-ins are shared, and every permission is denied; its scripts run while it loads, as in any browser, and it's then printed to PDF), and
• answer a question you ask in Ask AI. Only then, the document's text (up to about 400,000 characters), any passage you selected, and the conversation go to the provider you chose: OpenAI for ChatGPT, or Anthropic through your installed Claude Code. Their privacy terms apply to that data.

For ChatGPT, Folio stores its sign-in tokens in its data folder (below, under ai), encrypted with the system's credential protection (Windows data protection, the macOS Keychain, or the Linux secret store; if a Linux desktop has no secret store, you sign in again each time Folio starts), and never exposes them to the page. For Claude, Folio runs your own Claude Code with every tool disabled; it never sees or stores your Claude credentials. The question's context is written to a temporary file for Claude Code and deleted as soon as the answer finishes. Each document's Ask AI conversation is saved with it on this computer (except for password-protected documents) and is there when you reopen the document; the + button in the panel starts over and deletes it.

Stored locally in your user profile (%APPDATA%\Folio on Windows, ~/Library/Application Support/Folio on macOS, ~/.config/Folio on Linux): recently opened PDFs and their thumbnails (up to 8, removable from the home screen with Clear all; password-protected PDFs are never kept), highlights, notes, and Ask AI conversations for each document (except password-protected ones), reading positions, preferences, and, only if you choose to remember it, your signature image. Apart from the ChatGPT sign-in, this data isn't encrypted, so anyone with access to your user account can read it.

Building from source

Requires Node.js 22 or newer.

npm install
npm run app        # build and run the desktop app
npm run smoke      # end-to-end check: launches the built app and exercises the basics
npm run dev        # browser version with hot reload at http://localhost:5173

npm run dist:win   # on Windows: release/Folio-Setup.exe and release/Folio-Portable.exe
npm run dist:mac   # on macOS: release/Folio-mac.dmg (universal: Apple Silicon and Intel)
npm run dist:linux # on Linux: release/Folio-linux-x86_64.AppImage and release/Folio-linux-amd64.deb

Each platform's installers are built on that platform; GitHub Actions builds all three for every release. If your terminal has ELECTRON_RUN_AS_NODE=1 set, unset it first.

How it's put together

• src/: the reader UI (React + TypeScript, built with Vite) on top of pdf.js. markup.ts saves and restores highlights and notes, NotesPanel.tsx and Selection.tsx are their UI, and AiPanel.tsx is the Ask AI panel.
• electron/: the desktop shell for Windows, macOS, and Linux. main.cjs serves the built app from dist/ over a custom app:// protocol with a strict Content Security Policy, runs the page sandboxed with context isolation, opens PDFs from the file manager, keeps a single window, downloads links, and handles updates. webpage.cjs converts webpages to PDF. ai.cjs runs Ask AI (ChatGPT sign-in and requests, and Claude Code) so credentials never reach the page.
• scripts/release.mjs and .github/workflows/release-build.yml: the release pipeline (see CONTRIBUTING.md). scripts/smoke-test.mjs is the cross-platform smoke test CI runs. scripts/screenshots.mjs retakes the screenshots in this README (npm run build, then node scripts/screenshots.mjs).

Contributing

Bug reports and pull requests are welcome; see CONTRIBUTING.md. To report a security issue privately, see SECURITY.md.

License

MIT. Folio includes third-party software under its own licenses; see THIRD_PARTY_NOTICES.md.