PDF Annotator — Highlight, Draw and Comment Online
Add highlights, underlines, strikeouts, freehand drawings and sticky-note text to a PDF. Annotations are written as standard PDF annotation objects — every standards-compliant PDF viewer renders them correctly.
Drop your PDF file hereTap to select a file
Supports PDF, up to 100MB
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pdfAbout PDF Annotator
PDF Annotator is a self-contained PDF document workflow workspace. Add highlights, underlines, strikeouts, freehand drawings and sticky-note text to a PDF. Annotations are written as standard PDF annotation objects — every standards-compliant PDF viewer renders them correctly. Open the page, get the result, close the tab — that is the entire workflow.
Technically, the work is done by the open-source pdf-lib JavaScript library, loaded as part of the page. Inputs in PDF format are recognised automatically and validated before the engine begins processing. Files up to 100 MB are supported per run; that ceiling keeps browser memory usage stable on a wide range of devices.
PDF Annotator parses your file with the open-source pdf-lib JavaScript library entirely inside the browser, applies the options you selected, and returns a download. The processing has no network step, which means a slow or intermittent connection does not slow down the work — once the page is loaded, only your CPU and RAM are involved.
The heaviest users of PDF Annotator tend to be freelancers sharing scanned receipts, real-estate agents bundling disclosures and researchers archiving reference papers. Each group brings slightly different expectations to the tool, but the same single-page architecture serves every one of them with the same response time.
The right moment to reach for PDF Annotator is when you have a focused PDF document workflow job that fits inside a browser tab. Open the page, drop in the file or paste your input, choose the options that matter, and the tool returns the result.
The 100 MB ceiling on input size is the only fixed limit. Output files are produced in standard formats that every common viewer recognises, and the tool runs the same way regardless of how many times you have used it during the session.
PDF Annotator is intentionally narrow in what it does, which makes it easy to slot into a longer workflow. Take its output, hand it to whichever next tool fits the job, and PDF Annotator stays out of your way until the next time you need it.
PDF Annotator is honest about scope: it handles a single, well-defined PDF document workflow step. Specialist edge-case work — uncommon formats, very large inputs, or pipelines that need scripting — is what dedicated desktop apps are for. This page handles the common case quickly.
The download is delivered as `{name}-annotated.pdf` the moment processing completes — no email link, no "your result will be ready in 5 minutes" queue, no expiry timer. The file is generated in your browser and saved by your browser's normal download flow.
Some context on why PDF Annotator exists in this form: modern File APIs, high-performance JavaScript engines, and well-maintained open-source libraries now make it possible to perform PDF document workflow work entirely in the browser. PDF Annotator is built on top of that capability, which is why a single page can host the full pipeline.
If you also use a command-line tool for pdf annotator, PDF Annotator is a convenient alternative for the times you are on a different machine or helping someone who is not comfortable in a terminal. The output is a standard file in the format documented above.
If you want to get the most out of PDF Annotator, three small habits help. Drag-and-drop is faster than the file picker once you get used to it. The keyboard shortcut for downloading the result is whatever your browser uses for "save link as," because the result is a normal download. And if you are working on a sensitive file, processing in an Incognito or Private window is a good extra layer — it leaves no trace in browser history when the tab closes.
Common gotchas worth flagging: PDF Annotator only accepts PDF, so if your file is in another format you will need to convert it first. The 100 MB ceiling is per-file, not per-session; you can run as many separate jobs as you like, but a single oversized input will be rejected on load.
Open the workspace above to start using PDF Annotator. The engine loads on the first interaction so the page itself stays light, and once the tool is warm it processes subsequent jobs quickly. The moment the page is interactive, the tool is ready to do real work on your file.
How it works
- 1Open the PDF Annotator workspace above. The interface is a single page, so there is nothing to navigate.
- 2Select the PDF file you want to process — drag-and-drop and the file picker both work.
- 3Pick any non-default settings you need. Most users leave the defaults alone for the first run and only revisit if the result needs tuning.
- 4Trigger processing. the open-source pdf-lib JavaScript library reads your input, applies the transformation, and writes the result back into the page.
- 5Grab the output named `{name}-annotated.pdf` as soon as the run completes. You can also copy the result instead of downloading if the next tool in your workflow accepts pasted input.
- 6Run additional jobs as needed. The same controls and defaults apply on every run.
Common use cases
- Split a 200-page exhibit bundle into one PDF per exhibit using PDF Annotator.
- Shrink a scanned invoice so it fits past an email gateway.
- Send a polished, print-ready PDF to a client without watermarks.
- Extract a specific signed page from a long contract bundle.
- Strip blank or test pages from a scanned document.
- Rotate scanned pages that came in upside-down from the office scanner.
- Prepare a packet of receipts for an expense report submission.
- Lock a confidential document with a password before sharing externally.
FAQ
Which annotation types are supported?
Highlight, underline, strikeout, squiggly underline, freehand ink draw, sticky-note text, and rectangle / circle shapes. All are standard PDF annotation objects (subtypes Highlight, Ink, Text, Square, Circle).
Will the annotations work in standard PDF readers?
Yes — they are written as the standard PDF annotation objects defined in the PDF specification. Every standards-compliant PDF reader renders and edits them correctly.
Can I extract the annotations later?
Highlight passages can be extracted with PDF Highlight Extractor. Other annotation types can be inspected with PDF Inspector.
Will my PDF upload?
No. pdf-lib applies the annotation objects locally and the output is a fresh download.
Can I lock the annotations so reviewers cannot edit them?
Yes — chain the output through Flatten PDF and the annotations bake into the page content as immutable visual elements.
Which file formats does PDF Annotator accept?
PDF Annotator accepts PDF. If your input is in a format that is not directly supported, convert it first using one of Favtoo's converter tools — every Favtoo converter outputs a file that is a clean input to the next tool in the chain.
Why did PDF Annotator reject my input?
Failures usually fall into one of three buckets: the input is in an unsupported format, the input is over the size cap, or the input is structurally malformed (a truncated download, a partial export, or a stream the engine does not recognise). The first two are easy to confirm — check that your file is one of PDF and that it is below 100 MB. For the third, opening the file in its native viewer first is the fastest way to confirm the source is intact.
Is there a desktop version of PDF Annotator?
No installation is needed. PDF Annotator runs as a normal web page, with no browser extension, no native helper, and no separate desktop client to download. That is partly a privacy choice — extensions can request broad permissions, while a regular page is sandboxed by default — and partly a convenience one: you can use PDF Annotator on any computer you have temporary access to without leaving anything installed on it.
Can PDF Annotator run inside a corporate firewall?
PDF Annotator is a static page running an open-source engine in your browser, so a typical corporate firewall does not get in the way as long as it allows JavaScript to load from Favtoo. For teams that need to host it themselves on an internal network, the underlying engine (the open-source pdf-lib JavaScript library) is open-source and can be packaged into a private build with the same behaviour. Reach out via the Contact page if that is something you are exploring.
What does PDF Annotator do that command-line tools do not?
Desktop apps usually have more advanced features but require installation, maintenance and (often) a licence. Paid online tools are convenient but route your file through their servers and gate downloads behind accounts. PDF Annotator sits in between: free, instant, and private, but intentionally narrow in scope. For one-off jobs and the common PDF document workflow operations, it is usually the lowest-friction choice; for highly specialised work, a dedicated app is still the right answer.
Does PDF Annotator need an internet connection to run?
Once the page is loaded, PDF Annotator can complete jobs without an active internet connection — the engine is bundled with the page, so there is no per-job network call. The initial page load does require a connection (to fetch the static assets), but after that you can disconnect entirely and the tool will still work. This is a side-effect of the local-first architecture, not a deliberate "offline mode" feature.
How do I know I am using the latest version of PDF Annotator?
PDF Annotator is updated whenever the underlying engine releases an improvement or a bug fix. Because the tool is delivered as a static page, every visit fetches the latest version automatically — there is no "version" to manage on your end. If a particular release ever changes default behaviour, the change is documented on Favtoo's changelog so you can confirm what shifted.