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