Most "online PDF annotators" upload your file to their servers first. For contracts, research papers or anything private you probably don't want that. Here are the options that keep the PDF on your own computer.
Option 1: the browser's built-in PDF viewer
- Firefox has a built-in highlighter: open the PDF, click the highlighter icon in the toolbar, select text, then save with the download button. Your highlights are written into the saved copy.
- Edge has Highlight and Draw in its PDF toolbar.
- Chrome's viewer has had a basic drawing mode in some versions, but no text highlighter you can count on.
The catch: the highlights live only in the file you save. Close the tab without saving and they are gone, and nothing keeps track of which PDFs you annotated.
Option 2: a highlighter extension that handles web pages and PDFs
I built Glowmark for exactly this: one place for highlights on web pages and in PDFs, stored locally.
- Install Glowmark (Firefox; Chrome, Edge and Opera listings are in review).
- Right-click a PDF link and choose Open PDF in Glowmark, or use Open a PDF… in its side panel for a file on your computer.
- Pick the highlighter, pen or text tool and mark up the PDF.
The annotated copy is saved automatically in your browser and reopens next time; you can still download it. The PDF never leaves your computer, because Glowmark renders it with Mozilla's open-source PDF.js inside the extension. Web page highlighting is free; PDF highlighting is part of Glowmark Pro (7-day free trial).
Option 3: desktop apps
If you annotate PDFs all day, a desktop reader (Okular, Foxit, PDF-XChange, Preview on macOS) is worth it. For quick highlights while you browse, a browser tool is faster.
Disclosure: I'm the developer of Glowmark. Written with AI assistance, tested by hand.
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