Skim
free PDF reader and note-taker built for reading papers
Open source
Skim reads and marks up PDFs; it will not edit page content, run OCR or handle complex interactive forms, so it is a companion to a PDF editor rather than a replacement for one. Development is volunteer-driven and unhurried, which occasionally means waiting a few weeks after a macOS release. Most annotations are written as standard PDF notes, but some Skim-specific note data lives alongside the file, so export your notes before moving a library between machines or into someone else's hands.
Skim exists because reading a journal article is not the same job as editing a document, and the apps built for the second are bad at the first. It opens a PDF, gives you highlighting and margin notes that live in a sidebar you can export, and lets you tear off a snapshot window so the figure on page 4 stays visible while you read the methods on page 11. That one feature is why people who read papers for a living still have it installed twenty years on.
For anyone writing in LaTeX it goes further: SyncTeX support means command-click in the PDF jumps to the line in your source, and back again. It is also deeply scriptable, so a citation workflow can drive it from AppleScript.
The licence is BSD, the download is direct from SourceForge, and nothing in the app asks you for anything. What you do not get is editing — no changing page content, no OCR on a scan, no filling a fussy government form. Keep a separate tool for that.
If you read the occasional PDF and never annotate, Preview is already enough and installing this is pointless. The moment you are holding two hundred papers and need your own notes back out of them, Skim is the obvious first move.
What it looks like
What it does
- Highlight, underline and attach margin notes
- Notes sidebar that exports to text or Skim notes files
- Snapshot windows for comparing two parts of one paper
- SyncTeX jumps between a PDF and its LaTeX source
- Scriptable via AppleScript, and a full-screen presentation mode
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Also bought outright in documents
The facts
- Price
- Free
- Licence
- Free and open source
- What you get
- No licence to buy, and the source is public.
- Details
- Free and open source under a BSD licence, per the SourceForge project page. No paid tier, no donation wall, distributed as a direct download.
- Free trial
- No
- On Setapp
- No
- Minimum macOS
- macOS 10.13
- Developer
- Skim project
- Source
- Repository
- Price checked
- 2026-09-22
Check it yourself - Price band
- Free