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Okular vs Sioyek: catalog facts
Okular	Sioyek
Free Free and open source under the GPL.	Free Free and open source under the GPL. The developer accepts optional donations.
Windows, macOS, Linux	Windows, macOS, Linux
One viewer for a very wide range of document and comic formats Annotations are stored separately, so the original file is untouched	Opens a referenced figure, table or citation in an overlay without losing your place Searchable highlights, bookmarks and marks across your whole library
Pulls in KDE libraries on non-KDE desktops It is a viewer and annotator, not a PDF editor	The last tagged release is from December 2022 macOS shows a quarantine warning that needs working around on first launch
Downloadable app	Downloadable app
Open source	Open source
License: GPL-2.0	License: GPL-3.0
Not stated if an account is needed	No account needed
Not stated if it works offline	Works offline
Official website Full listing and sources Checked September 22, 2026	Official website Full listing and sources Checked September 21, 2026

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