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Best Free & Open Source Alternatives to PDF Expert

Compare 2 open-source PDF Expert alternatives including Koodo Reader and KillerPDF

If you're looking for the best open-source alternative to PDF Expert, Koodo Reader is a strong place to start. If it doesn't quite fit your needs, there are plenty of other great options worth exploring, including KillerPDF. We've ranked the top alternatives to help you compare your options and find the right fit.

#1 Koodo Reader

Koodo Reader

Cross-platform ebook reader supporting PDF, EPUB, MOBI, comics and more, with sync across Windows, macOS, Linux, Android, iOS, and Web.

What is Koodo Reader?

Koodo Reader is a free, open-source ebook and document reader that runs on Windows, macOS, Linux, Android, iOS, and the Web. It is built with Electron and TypeScript and supports a long tail of formats that includes PDF, EPUB, MOBI, AZW, FB2, DJVU, CBR/CBZ, TXT, Markdown, DOCX, HTML, and RTF. The app is aimed at readers who want one library that follows them across every device they own, without paying for a subscription.

Key features

  • Cross-platform parity: the same library, reading progress, highlights, and notes are available on desktop, mobile, and the web app.
  • Sync and backup to OneDrive, Google Drive, Dropbox, iCloud, MEGA, pCloud, Yandex Disk, Box, FTP, SFTP, WebDAV, SMB, or any S3-compatible object store.
  • AI tools: optional integration with custom AI models for translation, dictionary lookup, summaries, and an in-line encyclopedia, all running against your own keys.
  • OPDS catalogue support, plus a browser extension to save articles on the open web straight into your library.
  • Plugin ecosystem with 50+ built-in plugins for translation, dictionaries, OCR (Paddle and Tesseract), text-to-speech, and more.
  • Library features: bookmarks, notes, highlights exportable to CSV/Markdown/HTML/TXT/PDF, multi-level labels, snapshot/version-control, statistics, and password protection (with biometric unlock on supported devices).

Comparison to paid PDF software

Koodo Reader covers the same ground as Adobe Acrobat, Foxit Reader, PDF Expert, and Calibre (closed-source forks), but does it under an AGPL-3.0 licence with no premium tier and no advertisements. Unlike the paid readers, the mobile and web apps are full citizens of the same library, and cloud sync does not require a vendor account: you point Koodo Reader at any WebDAV or S3 bucket you control. Compared with PDF Expert for iOS or Adobe Acrobat Reader, the AI features are optional and self-hosted by default, the sync layer is end-user configurable, and the entire app remains usable fully offline.

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#2 KillerPDF

KillerPDF

Lightweight, fully portable PDF editor for Windows. Edit, merge, annotate, and sign PDFs locally with no subscription, accounts, or hidden telemetry anywhere.

KillerPDF is a local-only, portable PDF editor for Windows built for field techs and privacy-conscious users. It offers high-quality rendering via PDFium, inline text editing with font matching, annotation tools (highlight, freehand draw, text boxes), digital signatures, merge/split capabilities, and full-text search — all without an Adobe subscription or any phone-home telemetry.

The application is distributed as a single self-installing EXE (~6 MB zipped) that targets .NET Framework 4.8. On first launch it presents an Install or Run dialog; if installed, it goes per-user to %LOCALAPPDATA% with no UAC required, registers as a PDF file handler, adds a Start Menu shortcut, and can self-uninstall cleanly. Password-protected PDFs are supported, with the decrypted copy held in temp for the session.

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Frequently Asked Questions

Are there any open source alternatives to PDF Expert?

Yes, there are 2 open source alternatives to PDF Expert. Popular options include Koodo Reader, KillerPDF. These alternatives are free to use and many offer self-hosting options.

What is the best free alternative to PDF Expert?

The best free alternative to PDF Expert depends on your specific needs. Koodo Reader is a popular choice. All alternatives listed here are open source and free to use.

Can I self-host an alternative to PDF Expert?

Some alternatives may offer self-hosting options. Check each tool's documentation for deployment details.

Why should I switch from PDF Expert to an open source alternative?

Open source alternatives to PDF Expert offer several advantages: no vendor lock-in, complete data ownership, no subscription fees, the ability to self-host for privacy and security, and active community support. You can also customize the software to fit your specific needs.

PDF Expert

PDF Expert

PDF Expert is a paid PDF reader and editor from Readdle for macOS and iOS. It focuses on fast PDF viewing, annotation, form filling, and lightweight editing, and is widely used as the default PDF tool on Apple platforms.

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