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Skim vs PDF Expert: catalog facts
Skim	PDF Expert
Free Free and open source under the BSD licence.	Freemium Reading and basic annotation are free. Editing features require a paid plan.
macOS	macOS, iOS
SyncTeX integration makes it the standard viewer for LaTeX work Annotation and snapshot tools designed for reading academic papers	Genuine text and image editing inside the PDF, not just annotation Very fast on large documents, with a polished Apple-native interface
macOS only Notes are stored in Skim's own format unless explicitly embedded	macOS and iOS only Editing, OCR and conversion require a paid subscription or licence
Downloadable app	Downloadable app
Open source	Closed source
License: BSD-3-Clause	License not stated
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.