Skim

Skim is a free, open-source PDF reader and note-taking application for macOS, particularly useful for studying papers and other long documents. It helps you navigate, annotate and revisit PDF content; it is not a general-purpose document authoring suite or a promise to edit every element of a PDF.

Features

• Add and edit notes and highlight selected text.
• Navigate with thumbnails, contents, bookmarks and search.
• Keep selected document regions in snapshot windows for reference.
• Use a reading bar, magnification and full-screen reading.
• Present PDF slides in a dedicated presentation mode.
• Export notes and integrate supported PDF/TeX synchronization workflows.
• Automate supported operations through AppleScript and included command-line tools.

It suits researchers, students, reviewers and anyone who wants to read and annotate PDFs locally. Scanned image-only documents do not automatically become searchable text merely by opening them; available selection and search depend on the document's actual text content.

Install and compatibility

Install with brew install --cask skim, or download the official DMG and copy Skim.app to Applications. Open a PDF, select an annotation tool and save the document. The current official 1.7.17 page requires macOS 10.13 or later. The older SourceForge project summary still says 10.10; use the current version-specific website requirement. Skim 1.6 introduced native Apple Silicon support, and the project supports Mac desktop use on Intel and Apple Silicon; processor-compatible macOS versions still apply. It is not a Windows, Linux or iOS application.

The cask installs the app and links the bundled displayline, skimnotes and skimpdf tools. Normal PDF reading does not require a separate TeX distribution or BibDesk. Optional LaTeX/SyncTeX/PDFSync workflows require the relevant external editor, TeX build tools and synchronization data. Optional PostScript conversion has its own command/tool requirements, distinct from ordinary PDF viewing. The cask lists no additional formula dependency or explicit conflicting cask.

Saving annotations and sharing

Skim's native notes and highlights are normally stored as extended attributes attached to the PDF file, rather than inside the PDF data. Those attributes can be lost through email, archiving or file systems and transfer tools that do not preserve them. Saving successfully on the local Mac does not guarantee another PDF viewer or recipient will see the notes.

Export a separate Skim Notes .skim file for backup or transfer. Use the same base file name as the PDF so Skim can offer to import the notes when opening it. Other export choices include a PDF-and-notes bundle or PDF output with notes included; choose the format based on whether recipients need appearance compatibility or editable native Skim notes. Some sharing/conversion options lose native note capabilities or formatting. Test the exported copy in the recipient's viewer, and keep the original PDF and native notes before conversion.

Skim adds annotations and supports some document operations; it does not make every source document editable or remove password protection. Protected PDFs may limit viewing, selection, copying or modification. Use legitimate document passwords when required. The app supports saving PDF passwords in macOS Keychain, so consider whether to retain a password on a shared Mac.

Fonts, privacy and permissions

Text-note appearance uses the configured font and size, which can be changed through preferences and the font panel. PDF rendering also depends on the document and fonts available to the rendering system; there is no required Homebrew font package documented for normal installation. A missing or incorrectly encoded font in a document is not automatically repaired by installing Skim.

Reading and annotating a local PDF does not require a Skim account or a cloud upload. Remote-PDF downloads, update checks, external links and optional sharing/integration tools can use the network. Keep sensitive documents and exported notes in appropriate locations, review document links and scripts, and choose sharing destinations deliberately. File and automation access should be granted only for the workflow you use. The publisher does not document blanket Accessibility, Screen Recording or Full Disk Access as prerequisites for ordinary PDF reading.

AppleScript and configured synchronization commands can invoke external programs and are executable automation; use trusted scripts and sensible editor paths. Keep backups before scripts or conversion tools rewrite documents. Changing the default PDF viewer is optional and changes which app opens files, not the document format or compatibility with other readers.

Cost, license and download

Skim is free and open source under BSD-3-Clause terms in its official source license. No subscription, paid entitlement or online account is required for local reading and note-taking. Donations are optional, and included frameworks/components have their own notices.

The official 1.7.17 DMG is 10,422,451 bytes according to HTTP HEAD metadata from its SourceForge download mirror. Installed storage and document/notes storage differ. Review the official release notes when updating, especially fixes involving newer macOS PDF rendering and annotation behavior.

Sources: Official website, Official manual, Native notes export, FAQ, Font settings, Official license, Release notes.