PDF Annotator — Highlight & Draw on PDFs

Reading a PDF Is Passive — Annotating It Is Active

Marking up a PDF transforms it from something you read into something you work with. A highlighted passage stops being just text and becomes a reference point. A circled figure in a financial statement becomes an action item. A red underline in a contract clause becomes a question to raise in the next review call. Our free online PDF annotator gives you two direct tools for this — a highlight mode for area marking and a freehand draw mode for anything more expressive — across all pages of any PDF, without uploading your file anywhere.

Two Tools, Six Colours, Unlimited Pages

The Highlight tool creates semi-transparent colored rectangles. Click and drag across any area — text, a table, a chart, a diagram — and a 40% opacity color fill appears over it. This works on any visual element, not just text. The Draw tool gives you a freehand pen with adjustable brush size from 1px (precise hairline) to 12px (broad marker). Use it to circle items, draw arrows, underline specific words, write margin notes if your handwriting is legible on screen, or add freeform emphasis marks. Both tools support six colour swatches — yellow, orange, red, green, blue and purple — and you can switch colour between strokes without losing previous work. All annotations across all pages of the document are tracked in memory and included in the final download.

A Colour-Coding System That Actually Works

Consistent colour conventions make annotated documents dramatically more useful when you return to them later or share them with colleagues. A widely used approach: yellow for general interest and notable information; green for correct, confirmed or agreed items; red for errors, urgent issues or items requiring immediate attention; blue for definitions, key terms and technical references; orange for action items and follow-up tasks; purple for cross-references and related sections. Define your convention before starting a long annotation session and the resulting document becomes a structured summary of your analysis, not just a mass of random marks.

How Annotations Are Embedded in the Downloaded PDF

When you download, pdf-lib converts canvas pixel coordinates back to PDF point coordinates and draws each annotation as a permanent element in the page content stream. Highlights become filled rectangles with 40% opacity. Pen strokes become sequences of line segments. This content-layer approach is fundamentally different from PDF annotation objects (sticky notes, markup comments) — our annotations have no annotation panel, cannot be toggled off, and display identically in every PDF viewer on every platform including mobile. They also appear in print exactly as they look on screen.

Practical Uses Across Different Fields

• Legal contract review: Circle problematic clauses, highlight defined terms, underline conditions that need negotiation — share the annotated version with the counterparty or your own team for discussion
• Academic research: Colour-code findings by theme across journal papers, highlight methodology sections, mark data points for extraction — after annotating, use our PDF to Text tool to extract raw text for quoting or note-taking
• Financial document analysis: Circle unusual figures in statements, highlight key ratios, draw attention to footnotes during due diligence reviews
• Study and exam preparation: Highlight lecture notes by topic, circle formulas, mark sections for revision, build a colour-coded visual index across multiple documents
• Design and visual feedback: Circle layout problems in PDF mockups, draw arrows pointing to alignment issues, mark areas that need image replacement — for actually adding images to a PDF, use our Add Image to PDF tool
• Document proofreading: Underline grammatical errors, circle inconsistent formatting, highlight sections that need rewriting before the document goes to print

Navigating Multi-Page Documents

The navigation bar above the canvas lets you move between pages with Prev/Next buttons or by typing a page number directly. Zoom controls (+ and −) adjust the canvas scale from 50% to 300% so you can work at the right level of detail — zoom in for precise highlighting of small text, zoom out for an overview of a full page. All annotations are stored per page in memory as you navigate. The annotation counter in the stats row shows total annotations and the count for the current page so you always know how much you have marked up.

100% Browser-Based — Nothing Transmitted

The annotator runs entirely in your browser using PDF.js for rendering and pdf-lib for output generation. Your PDF file, its page renders and every annotation coordinate stay on your device throughout. Nothing is uploaded to ToollyX or any third party at any stage. This makes the tool safe for annotating legally privileged documents, patient records, confidential financial filings, proprietary research and any document you would never upload to a cloud annotation service.

✓Verified by ToollyX Team · Last updated June 2026