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Skim vs Preview: catalog facts
Skim	Preview
Free Free and open source under the BSD licence.	Free Included with macOS at no extra cost.
macOS	macOS
SyncTeX integration makes it the standard viewer for LaTeX work Annotation and snapshot tools designed for reading academic papers	Already installed on every Mac Handles both PDFs and images
macOS only Notes are stored in Skim's own format unless explicitly embedded	macOS only No advanced editing of PDF text or OCR tools like dedicated editors
Downloadable app	Downloadable app
Open source	Closed source
License: BSD-3-Clause	License: Proprietary
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 24, 2026

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