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How to Annotate a PDF: Highlights, Notes and Drawing

How to annotate a PDF: highlights, notes, text, drawings and stamps, how annotations differ from page content, and why a black box is not a redaction.

By Published 4 min read

Reign Creative LLC makes PDF All in One Tool No Limit, which this article links to, so we have a commercial interest in it. How we write and check articles.

AI-assisted article. Drafted with AI tools from the sources cited below and checked by automated tests and an AI editorial review. No person has reviewed it yet. How we write and check articles.

Key takeaways

  • Annotations, such as highlights, notes, text, drawings and stamps, sit on top of a PDF's pages rather than changing the page content.
  • That makes annotations easy to add and remove, and ideal for review: the original stays intact underneath.
  • Wikipedia notes that text covered with black rectangles in a PDF remains in the file and can be recovered by deleting the overlay.
  • Wikipedia adds that effective redaction requires removing all the relevant text and image data from the file, so use a real redaction tool, not a drawing.
  • Use a consistent system: one highlight colour for issues, another for questions, and notes for anything that needs words.

Annotating is the PDF version of a pen in the margin: highlight what matters, write a note, circle a mistake, stamp "approved". It is how documents get reviewed, studied and corrected. This guide covers the main annotation tools, how annotations differ from the page itself, and the one mistake that turns markup into a data leak.

Annotations sit on top of the page

Wikipedia's PDF article reflects a separation between a page and the marks made on it in two places: the permissions an author can restrict list adding or modifying text notes separately from modifying the document, and the XFDF format can carry a document's forms and annotations as data on their own. That separation is the key idea: an annotation is a layer on top of the page, not a change to it. You can add a highlight, delete it and the text underneath is exactly as it was.

The main tools

Tool What it is for
Highlight Marking passages that matter
Note or comment Explaining something without changing the page
Text Adding words on the page, such as a label or a correction
Drawing or pen Circling, underlining or sketching freehand
Marks and stamps Ticks, crosses or a standard stamp such as "approved"

PDF All in One Tool No Limit includes annotation tools for text, notes, highlights, drawings, marks and stamps; its Google Play listing mentions using them to review a document before sending it. Tool names and menus differ between apps and app versions, so treat the table above as the kinds of tool to look for.

Annotating for study

For reading and revision, annotations work best with a simple system:

  1. One colour for key points, another for things you do not understand.
  2. Notes for summaries: a one-line note at the top of each section saves rereading.
  3. Drawings for connections: an arrow linking a definition to the example that uses it.

Fewer, deliberate marks beat a page highlighted from top to bottom.

Annotating for review

When marking up someone else's document, the aim is that they can act on every mark without asking you what it means:

  • Point and explain: highlight the text and add a note saying what is wrong and what you suggest.
  • Be specific: "total on page 4 does not match the table on page 6" beats "check numbers".
  • State your colours at the top, for example yellow for questions and red for errors.
  • Send the annotated copy and the clean original, named so they cannot be confused.

Annotating on a small screen

A phone makes markup fiddly, so a few habits help:

  • Zoom before you mark: highlights land more precisely on enlarged text.
  • Use a stylus for drawings, or turn the phone sideways for a wider page.
  • Use undo freely rather than erasing mark by mark.
  • Write notes, not essays: long comments are easier to read as a short summary note at the start of the document.
  • Save regularly, so an interruption does not lose a review session.

A worked example: one contract, three passes

You receive a 12-page agreement to check. Pass one: highlight every date, amount and deadline in one colour, which gives you a map of the obligations. Pass two: add a note to each highlight that does not match what you agreed. Pass three: stamp or mark the pages you accept. The result is a document the other party can work through note by note, and your clean copy is untouched for signing later.

A black box is not a redaction

The layer that makes annotations convenient also makes them dangerous for hiding information. Wikipedia's article on redaction explains that where text in a PDF or word-processing file is covered by overlaying graphical elements, usually black rectangles, the original text remains in the file and can be uncovered by simply deleting the overlay. It adds that effective redaction of an electronic document requires the removal of all relevant text and image data from the file. Hidden data is not only under black boxes: the Federation of American Scientists' summary of the US National Security Agency's December 2005 guidance, Redacting with Confidence, quotes its warning that merely converting a Word document to PDF does not remove all sensitive metadata automatically.

So never use a drawing, highlight or stamp to hide an account number or a name. Use a dedicated redaction tool that removes the underlying text, or send only the pages that are needed; how to split a PDF covers extracting pages, and password-protecting a PDF covers access.

Annotations and forms

If a document has fields to complete, fill them in rather than writing over them; filling in a PDF form explains the difference between form entries and annotations.

PDF All in One Tool No Limit is one of our video and utility apps; its guide covers the rest of its tools.

Good to know

Frequently asked questions

How do you annotate a PDF?
Open it in a PDF app with markup tools, then select text to highlight it, add sticky notes or text comments, draw with a pen tool, or place stamps and marks. Save the annotated version as a new file so the clean original remains.
What is the difference between annotating and editing a PDF?
Annotating adds marks on top of the page, such as highlights and comments, which can be removed later. Editing changes the page content itself, such as the underlying text or images. Wikipedia's PDF article lists adding or modifying text notes as a permission separate from modifying the document.
Does drawing a black box over text in a PDF hide it?
Only visually. Wikipedia notes that when text in a PDF is redacted by overlaying black rectangles, the original text remains in the file and can be uncovered by deleting the overlay. Proper redaction removes the underlying text.
How should I mark up a PDF for someone else to review?
Use highlights to point at text, notes to explain, and one or two colours with a stated meaning. Keep comments specific, such as 'figure on page 4 does not match the table on page 6', and send the annotated copy alongside the clean original.

Sources

  1. PDF (opens in a new tab)Wikipedia — accessed
  2. Redaction (opens in a new tab)Wikipedia — accessed
  3. NSA: Redacting With Confidence (opens in a new tab)Federation of American Scientists — accessed

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