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Skim vs Okular: catalog facts
Skim	Okular
Free Free and open source under the BSD licence.	Free Free and open source under the GPL.
macOS	Windows, macOS, Linux
SyncTeX integration makes it the standard viewer for LaTeX work Annotation and snapshot tools designed for reading academic papers	One viewer for a very wide range of document and comic formats Annotations are stored separately, so the original file is untouched
macOS only Notes are stored in Skim's own format unless explicitly embedded	Pulls in KDE libraries on non-KDE desktops It is a viewer and annotator, not a PDF editor
Downloadable app	Downloadable app
Open source	Open source
License: BSD-3-Clause	License: GPL-2.0
Not stated if an account is needed	Not stated if an account is needed
Not stated if it works offline	Not stated if it works offline
Official website Full listing and sources Checked September 22, 2026	Official website Full listing and sources Checked September 22, 2026

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