Annotate · Markup

Annotate PDF Files Online Without Uploading Them

Highlight, comment, draw, and stamp on a PDF directly in your browser. Annotations save to a standards-compliant PDF that any viewer can open — and the original file never leaves your device.

If you want to annotate PDF files online — mark up a contract, review a research paper, or leave comments on a draft — without sending the document to a review portal or a server, PDF Pro does the whole workflow locally in your browser. The markup tools write real PDF annotations (not image overlays), so the resulting file opens correctly in Adobe Acrobat, Preview, or any standards-compliant reader. Got several files to review in one pass? Combine them into a single PDF first → and annotate everything in one workspace.

memoryRuns in your browser verifiedStandards-compliant output brushHighlight · comment · draw · stamp blockNo signup, no watermark
drawOpen the Annotator How it works

Why server-side annotation is awkward

Most "online PDF editor" tools upload your PDF, render pages to images on their server, capture your annotations as overlays, and compose a new PDF when you're done. That flow has three costs worth knowing about.

Three trade-offs of the server-side model

  1. Your file sits on their server for the duration of the session — which for a long review is measured in hours, not seconds.
  2. Annotations become images, not structured PDF objects. The text you typed can't be selected, searched, or extracted downstream.
  3. The file grows unnecessarily because every marked-up page is re-rasterized.

PDF Pro takes the opposite approach. The viewer is the browser's own PDF engine, your annotations are written into the PDF as proper annotation objects (highlights, text notes, ink, shapes), and the output is a standards-compliant PDF — smaller, selectable, and interoperable with any reader.

What this is good at

Four things the in-browser annotator gets right that typical server-side markup tools don't.

verified
Clean PDF output — any reader opens it
Annotations render into the saved PDF as part of the document. Adobe Acrobat, Preview, Foxit, or any modern viewer opens the result — no PDF Pro account, no proprietary viewer needed.
build
A complete review toolbox
Highlight, underline, strikethrough, freehand ink, text boxes, sticky notes, shapes, and stamps. Everything you'd reach for during a contract review or paper markup.
cloud_off
Pages never leave your device
The PDF is opened from disk into your browser, annotated in-tab, and saved back to disk as a local download. No round-trip.
share
Reviewer-friendly output
The recipient doesn't need PDF Pro or any account to see your comments. Adobe Reader opens it. Preview opens it. Any modern PDF viewer opens it.

How it works

Four steps from a blank PDF to a marked-up file you can share.

1
Drop the PDF
Drag a file in or click to pick one. The file is read locally — no upload.
2
Pick a tool and mark up
Highlight a sentence, draw a rectangle around a figure, drop a sticky note, or stamp "Approved" in a corner. Colors, line thickness, and opacity are adjustable.
3
Manage annotations
The side panel lists every annotation with its page number. Click to jump to it, edit comment text, or delete. Everything stays editable until you save.
4
Save locally
Save a new PDF with your annotations baked in. The file downloads straight to your disk and opens cleanly in any reader.

Real use cases

Workflows where a real PDF annotator makes more sense than a dedicated review platform.

Contract review before countersign
Highlight risky clauses, drop a comment asking for a change, and send back — without the document going through a third-party annotation service.
Research-paper markup for a collaborator
Underline the claim you want to discuss, add a sticky note with your question, and share the annotated PDF. Your co-author can reply with their own annotations in any reader.
Design-document review
Draw circles around UI elements, add text callouts, and stamp pages that need redesign — all without exporting to a separate review platform.
Teacher feedback on student work
Mark up a submitted PDF directly, save with annotations, and send back. No tokens, no portals, no account creation for the student.

Honest limitations

  • Scanned / image-only PDFs have no text layer. Highlight and underline need selectable text. If the PDF is a scan, you can only draw shapes, type text boxes, or stamp — not highlight specific words.
  • Saved annotations are not editable in other PDF readers. Annotations are rendered into the saved PDF as part of the document. A reviewer opening the file in Acrobat or Preview sees exactly what you saved, but can't move or remove your marks from there — re-edit from a pre-annotation copy if you need that flow.
  • Encrypted PDFs must be unlocked first. We don't bypass owner passwords. Unlock the file in your reader, then annotate.
  • Digital signatures break on edit. Annotating a signed PDF invalidates its signature — this is the whole point of PDF signatures. Annotate before signing, not after.
  • Form-field interactions can be fragile. Annotating a PDF with an active form is supported, but some reader-specific form behaviors may not be preserved round-trip. Flatten forms first if in doubt.
  • Large documents feel slower. 500+ page PDFs take longer to render a preview of every annotation in the side panel. Performance is acceptable, not instant, at that scale.

Why PDF Pro instead of other annotation tools

Four differences that show up in the actual review workflow.

memory
Local, not uploaded
Most online annotators upload. We run in-tab — verifiable in DevTools.
verified
Standards-compliant output
Your annotations are real PDF objects, not baked-in image overlays. Downstream readers can work with them normally.
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No per-file or per-page gating
Annotate a one-page memo or a 300-page spec. No signup, no watermark, no "unlock extended features" wall.
sync
Stays in one workspace
After annotating, the file is still in the workspace — sign it, compress it, convert it, or share it without re-uploading.

Related tools

What pairs naturally with an annotation workflow.

Overview first
Run an AI summary to decide which sections deserve close attention.
Ask about a clause
Chat with the document to let the AI pull the relevant paragraph.
Extract marked-up text
Convert the annotated PDF to an editable Word version.
Shrink before sending
Compress without losing readable text after annotation.
Export annotated pages as JPG
Turn marked-up pages into standalone images for slides or uploads.

Sending a sensitive reviewed document? Use a end-to-end encrypted link instead of an attachment. Want the annotated pages as images for a deck? Turn the PDF into image format once the markup is final.

Frequently asked questions

Is my PDF uploaded when I annotate it?
No. The annotator reads the file locally, writes annotations in-browser, and saves the result as a local blob download. Verify in DevTools → Network — no upload happens.
Can someone using Adobe Acrobat open my annotations?
Yes. Annotations are rendered into the saved PDF as part of the document content, so Acrobat, Preview, Foxit, and any modern viewer display them exactly as saved. Your recipient doesn't need PDF Pro.
Can I edit or remove an annotation after saving?
Within the session, yes — the annotation sidebar lists every mark you've placed and you can edit or delete individual entries before saving. Once you save and re-open the PDF, annotations become part of the document. To change them later, edit the original (pre-annotation) PDF and re-annotate.
Does annotation work on scanned PDFs?
Partially. Drawing tools, stamps, text boxes, and sticky notes all work. Text-level tools (highlight, underline, strikethrough) need a selectable text layer, which a raw scan doesn't have.
Do my comments get saved in the cloud?
No. There is no cloud component for the annotation tool. The annotated file is a local download; its only backup is wherever you save it.
Will annotating break the PDF's digital signature?
Yes. Any edit to a signed PDF invalidates its signature — this is how PDF signatures are defined to work. Annotate first, sign last.
Can I annotate the same PDF collaboratively in real time?
No. PDF Pro is single-user per session. For async collaboration, save your annotated copy, send it to the other person, and let them add their annotations in their own session.
Does annotation add a watermark to the output?
No. The output is a clean PDF with the annotations you placed and nothing else.
How big can the PDF be?
No hard cap. Practical limits are your browser's memory — files up to a few hundred MB work on a typical laptop. Very large technical-drawing PDFs can slow the page-switching UI.

Mark up your PDF without sending it to a review portal.

Open the annotator, highlight what matters, drop comments, download the marked-up file. No account, no upload, no watermark.

drawOpen the Annotator