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