How do I annotate a PDF online for free?

Open PDFFlare's Edit PDF tool in any browser, drop your PDF, and use the toolbar to add highlights, sticky notes, freehand drawings, text overlays, and shapes. Each annotation type has its own tool — pick highlighter, pen, text, sticky note, or shape, then drag on the page to place it. Save when done; annotations are flattened into the saved PDF so anyone who opens it sees your markup. Free, browser-based, no install, no signup, no upload.

How do I highlight text in a PDF?

Pick the highlighter tool in PDFFlare's Edit PDF, drag across the text you want to highlight, release. The highlight wraps to the text shape automatically. Default color is yellow at 50% opacity; switch colors for category coding (yellow = notable, pink = needs follow-up, green = approved). For column-aware highlighting that skips margins, drag line by line. For full-line highlighting, drag across the whole line at once.

How do I add sticky notes to a PDF?

Pick the sticky note tool, click anywhere on the page where you want the note, type your comment in the popup. The note appears on the page as a small icon; clicking it expands to show the comment. Useful for margin observations during contract review or proofreading without cluttering the visible content. PDFFlare flattens the comments into the saved PDF so they appear in any PDF reader, not just PDFFlare's tool.

Can I draw on a PDF with Apple Pencil on iPad?

Yes — PDFFlare's Edit PDF tool works in iPad Safari with full Apple Pencil support. The pen tool detects pressure for variable-width strokes (so signatures and handwriting look natural), and the highlighter snaps to text just like on desktop. Or use Markup (built into iPadOS) for one-tap annotation if the PDF is already open in Mail or Files — Markup is faster for quick markup, while Edit PDF gives you more tool variety and finer control.

Will my annotations show up when others open the PDF?

Yes — PDFFlare's Edit PDF flattens annotations into the saved PDF by default, so they're baked into the page content stream and appear in every PDF reader (Adobe Acrobat, Preview, Chrome, Edge, mobile readers). Recipients can't toggle annotations off or remove them without specifically editing the PDF. This is different from layered annotations in some tools, which can be hidden or removed by readers.

May 7, 20268 min read

How to Annotate a PDF (Highlights, Notes, Drawings) — Free

You're reviewing a contract, marking up a research paper, or proofreading a manuscript. The traditional options are paper printouts with a red pen, or paid tools like Adobe Acrobat for $25/month. The third option — annotate a PDF online free in your browser using PDFFlare's Edit PDF tool — gives you the speed of digital with the flexibility of paper, without the subscription.

In this guide you'll learn how to annotate a PDF with highlights, sticky notes, freehand drawings, and text overlays — all in your browser, with the file staying entirely on your machine. The flow is the same on Mac, Windows, iPad, and Android Chrome.

What Counts as Annotation?

PDF annotations are markup layered on top of the document content — they don't change the underlying PDF text. The major annotation types:

Highlights — translucent color overlays on text. Yellow is universal; pink, green, blue used for category coding.
Sticky notes / comments — small icons that pop open with text when clicked. Used for margin observations and review feedback.
Underline + strikethrough — for indicating emphasis or deletion.
Freehand drawing — for circling, arrows, stars, signatures, or hand-drawn margin notes.
Text overlays — typed text added on top of the page (different from filling in form fields).
Shapes — rectangles, ovals, lines for framing important regions.

How to Annotate a PDF (Step by Step)

Open Edit PDF. Visit /tools/pdf/edit-pdf and drop your PDF.
Pick the annotation tool from the toolbar — highlighter, pen, text, sticky note, shape.
Drag over the page to place the annotation. Highlighter wraps around text; pen draws freehand; text inserts a typed overlay; shapes box a region.
Adjust color and opacity in the tool options. Highlights default to yellow at 50% opacity — change for category coding (e.g., pink for objections, green for approvals).
Repeat across pages. Use the page navigator to jump between pages; annotations attach per-page.
Save the annotated PDF. Annotations are baked into the saved file — anyone who opens the result sees the markup.

Annotation Tips by Use Case

How to highlight text in a PDF

Use the highlighter tool, drag across the text region, release. The highlight wraps to text shape. For column-aware highlighting (skipping margins), drag line by line; for full-line highlighting, drag across the whole line. Use color-coding for category review: yellow for “notable,” pink for “needs follow-up,” green for “approved.”

How to add sticky notes (comments) to a PDF

Pick the sticky note tool, click anywhere on the page, type your comment. The note appears as an icon on the page; clicking it pops open the comment text. Useful for margin observations during review without cluttering the visible page. PDFFlare flattens the comments into the saved PDF so they appear in any PDF reader (not just PDFFlare).

How to draw on a PDF online free

The pen tool lets you draw freehand — circles, arrows, stars, hand-drawn margin notes. On iPad, Apple Pencil captures pressure for natural-looking strokes. On desktop with a mouse, draw slowly for smoother curves. Use a thin line width (1-2px) for fine markup; thicker (5-10px) for emphasis.

How to annotate a PDF on iPad

PDFFlare's Edit PDF works in iPad Safari with full Apple Pencil support. Pen tool detects pressure for variable line width; highlighter snaps to text. The same workflow as desktop, but with handwriting-quality strokes. Or use Markup (built into iPadOS) for one-tap annotation if the PDF is already open in Mail or Files — see our companion post on signing PDFs on iPad.

Annotation Workflows by Document Type

Different documents call for different annotation patterns:

Contract review: highlight the clauses you want to question (yellow), strike-through the ones you want removed (red), add sticky notes explaining why. Send the marked-up copy back to legal as your redline.
Research paper / academic reading: highlight key claims (yellow), questions you have (pink), things to follow up (green). Add margin notes with the pen tool for full sentences. Re-read the highlights as a study guide.
Manuscript proofreading:circle typos, highlight phrases that need rewording, sticky-note substantive feedback. Send back as the “edits” file alongside the original.
Form review before signing: highlight blanks the recipient must fill, add a sticky note at the top with high-level instructions, mark the signature line with a circle. Send to the signer.

Common Mistakes

Highlighting the whole page. Universal highlighting tells the reader nothing. Highlight selectively — 5-15% of the text per page max.
Mixing tool styles inconsistently. If yellow = “noted,” stick with yellow for that meaning across the document. Inconsistent color usage confuses the reader.
Forgetting to flatten before sharing. By default, PDF annotations are a separate layer that some readers can hide. PDFFlare's Edit PDF flattens annotations into the saved PDF so they can't be turned off — anyone who opens the file sees your markup.
Annotating a scanned PDF without OCR first. The highlighter snaps to text regions; on scans (where text is bitmap), it has nothing to snap to. Run OCR PDF first to add a text layer.

Privacy: Annotate Without Uploading

PDFFlare's Edit PDF tool runs entirely in your browser via pdf-lib and Fabric.js. Your PDF, your annotations, and the saved result all stay on your machine — no server is involved. Open DevTools → Network while annotating and you'll see zero requests to PDFFlare. Important when reviewing confidential contracts, legal documents, or internal-only materials.

Related Tools

Edit PDF — annotate, highlight, draw, comment. Browser-based, no upload.
Sign PDF — annotation flow ends with a signature; this tool handles the signature step.
OCR PDF — run on scanned PDFs before annotating so the highlighter can snap to text.
Merge PDF — combine annotated copies from multiple reviewers into one consolidated document.

Wrapping Up

Annotate a PDF online free without installing anything: open PDFFlare's Edit PDF tool, drop the file, mark it up with highlights, sticky notes, drawings, and text overlays. Save. Share. The whole flow runs in your browser without uploading, which matters for confidential documents and internal review work.