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Stirling PDF vs PDF4QT: catalog facts
Stirling PDF	PDF4QT
Freemium Free plan is $0/month with no card required (60+ tools, web/desktop/self-hosted, 500…	Free Free and open source; donations are accepted through GitHub Sponsors.
Windows, macOS, Linux, Web, Self-hosted	Windows, Linux, Command line
55+ PDF tools covering signing, converting, merging, editing, OCR and redaction, chained in a stateful workspace with… Runs on Docker, bare metal, Kubernetes or as native desktop apps for Windows, macOS and Linux	Viewing and editing applications in one project Command-line tool for scripted PDF work
Open-core: SSO, external database, Google Drive integration, SAML and audit logs are gated behind paid Team or… Manual server setup needs Java 25+ plus LibreOffice and Tesseract for conversions and OCR	No macOS version Mostly the work of a single principal developer
Self-hosted, Downloadable app, Web application, Hosted service	Downloadable app
Open source	Open source
License: MIT	License: MIT
No account needed	No account needed
Works offline	Works offline
Official website Full listing and sources Checked September 20, 2026	Official website Full listing and sources Checked October 1, 2026

Catalog facts only. Anything “not stated” is unconfirmed. Check full listings for details.