Annotate PDF online

What Annotate PDF does

Annotate PDF is for marking up a PDF while you review it: highlighting important lines, circling problems, underlining words and writing notes for a colleague, teacher or client. The default color is yellow, which works well for highlights.

When you click Save PDF, pdf-lib draws your marks into the page content. They are not stored as separate PDF comment objects, so they look the same in every viewer and print exactly as shown, but other apps do not list them in a comments panel.

How to use Annotate PDF

1. Drop the PDF you want to work on.
2. Choose a tool from the toolbar and click on the page to use it.
3. Move, resize or delete anything you added before saving.
4. Click Save PDF to download the result.

When to use Annotate PDF

• Highlight key clauses in a contract or lease and add notes with questions before discussing it with a lawyer.
• Mark corrections on a student essay or thesis draft, then send the annotated PDF back to the student.
• Circle errors on a design proof or print layout and write what needs to change for the designer or print shop.
• Highlight important passages in lecture slides or a research paper while studying for an exam.

Settings explained

Highlight

Drag a box across text to cover it with a see-through color at 40 percent opacity. A single click creates a short highlight bar. The tool stays active, so you can mark several lines in a row.

Draw

Draw freehand with a mouse, finger or stylus to underline, circle or cross out content. The line thickness is a quarter of the Font size value, with a minimum of 2 points.

Note

Click to add a yellow note box with room for a few lines of text. The note is printed on the page itself, so place it in a margin or an empty area where it does not hide content.

Text

Adds plain text in the selected color without a background. It is useful for short labels, page references or corrections written next to the content.

Rectangle

Drag to draw a rectangle outline, for example around a table or paragraph. Ellipse draws an oval outline, which works well for circling a number or word. Both use a 2-point border.

Color

The color picker in the toolbar sets the color for new marks; select an existing mark to change its color. Yellow suits highlights, red works well for corrections, and blue or black for written comments.

What is PDF?

PDF (Portable Document Format) is a document format introduced by Adobe in 1993. Files use the .pdf extension.

PDF was created by Adobe to show documents the same way on any device and printer. A PDF file describes pages with text, fonts, vector graphics and images at fixed positions. It became an open ISO standard in 2008, and there are special variants such as PDF/A for archiving and PDF/X for printing.

PDF is the right choice for documents that must look the same everywhere, such as contracts, invoices, forms, manuals, reports and files for printing. It also supports digital signatures, fillable forms, comments and password protection.

PDF is hard to edit, because text is stored as positioned pieces, not as flowing paragraphs. Converting a PDF to Word may change the layout. Scanned PDFs contain pictures of text, not real text, unless OCR has been applied.

All major web browsers open PDF files directly. Windows, macOS, iOS and most Android phones include a PDF viewer, and Adobe Acrobat Reader and many free apps can view, annotate and fill PDF forms on all platforms.

Why use FansBond Annotate PDF

Most online converters upload your files to their servers. FansBond Annotate PDF does the work inside your browser instead, using WebAssembly and modern browser APIs. Your files stay on your device, which is safer for private photos, contracts and unreleased work, and it is often faster because nothing has to upload or download.

There are no queues, no watermarks and no account. Once the page has loaded, the tool keeps working even on a slow connection.

Tips for the best result

• There is no separate underline tool. Use Draw for underlines and strikethroughs, or drag a thin Highlight box under a line of text.
• Yellow text is hard to read. Choose a darker color before you add Text or Draw marks, and switch back to yellow for highlighting.
• Undo removes the last mark you added. To remove a specific mark, choose Select, click the mark and press Delete.
• Marks become part of the page after saving, so keep a clean copy of the original PDF if you need an unmarked version later.

How Annotate PDF works in your browser

Each page is rendered with pdf.js so you can see it and place items exactly. What you add is kept as separate objects until you save, so you can move, resize or delete it at any time.

When you save, pdf-lib writes your text, drawings, images and fields into the original PDF. The original page content is not re-rendered, so existing text stays sharp and selectable.

Privacy and security

Most online converters upload your files to a server, process them there and keep a copy for some time. Annotate PDF works differently: the code is downloaded to your browser once, and your files are read and written only on your device.

You can check this yourself: after the page has loaded, turn off your internet connection and the tool still works. This makes it safe for contracts, IDs, medical records, private photos and unreleased work.