How to Annotate a PDF Online

How to Add a Note to a PDF Page

Sending a colleague a document and explaining what is wrong with it works better on the page itself than in the body of an email. The note tool does exactly that: it draws a yellow sticker with your text over the pages you pick. What matters is understanding what you get out of it, because the word "annotation" here means something other than it does in a reader.

It is a stamp, not a comment

The PDF comments everyone knows from Acrobat and from browser viewers are separate objects inside the file. They can be opened, collapsed, replied to, marked resolved and deleted without touching the page.

The note this tool places is built differently. It is drawn straight into the page content: a rectangle, a border and text. No comment object appears in the file at all, which is verifiable on the finished result: the page's annotation list stays empty.

Three practical consequences follow, and they are worth weighing before you send anything.

The note is visible to everyone everywhere: in a browser, on a phone, in a document management system that does not show comments. Nothing has to be switched on, and nothing can fail to render.

The note prints. An ordinary comment does not print by default; this one is part of the page.

The note cannot be removed without redoing the document. Neither the recipient nor you can take it off with a click; that would need the original file. So work on a copy, not on your only version.

Where the sticker lands

The position is given as fractions of the page rather than millimetres, so the same set of numbers behaves identically on A4 and on A3.

The vertical is measured from the top, not from the bottom. That is worth remembering: a value of 0.9 drops the note near the bottom edge rather than raising it to the top.

Both offsets are capped at 0.95, so the sticker cannot be pushed off the page. The width is trimmed at the right edge too: a sticker that does not fit ends at the edge of the sheet instead of running past it.

There is a lower size bound as well, roughly 32 by 14 millimetres. A smaller sticker cannot be requested even with tiny fractions: a rectangle too small to hold text is of no use.

The defaults put the sticker in the upper left quarter of the page, across half its width. On a document with ordinary margins that is above the first paragraph or right on it. If the content there matters, move the sticker into the margin or down the page rather than relying on its translucency.

How to place the note

1. Open annotate-pdf and upload the document. 2. Mark the pages that need the note on the preview grid. 3. Type the text. Short works better, and the next section explains why. 4. Adjust the sticker's position and size if you need to. 5. Run the job and download the result. 6. Open the file and read the note through. All of it.

Long text is truncated in silence

This is the tool's main trap. The text wraps by words inside the sticker, and the lines that do not fit vertically are simply not drawn. No warning, no ellipsis, no hint that part of the text stayed out of frame.

Tested with a long note at different sticker sizes:

Both dimensions work, but differently. Width adds characters to a line and nothing else. Height adds both lines and type size: the font is computed from the height until it hits its ceiling of 18 points. So a wide, shallow sticker holds a lot of small text, while a tall, narrow one holds less of it, larger.

Two rules follow. Write short: one thought, two lines at most. If the text does run longer, grow the sticker in both directions at once, since each one alone buys roughly half as much.

And always open the result. A note cut off mid sentence looks finished, and the loss is noticeable only from the meaning.

Colour and font are not configurable

The sticker is always the same: a translucent pale yellow fill, an amber border a point and a half thick, dark brown text. Neither colour nor opacity appears in the parameters.

The fill lets through about half of what is under it, so the text beneath the sticker stays legible. That is convenient when the note concerns a particular paragraph and should sit beside it, but it also means the sticker cannot be used to cover anything.

The font size is not set either. It is derived from the sticker's height and bounded between 8 and 18 points. At the default settings you get the upper bound, 18 points, noticeably larger than the document's body text, and that is deliberate.

One note across every selected page

One text is written and placed on every marked page at the same point. Different notes on different pages in a single pass are not available.

If that is what you need, there are two routes. Run the document through several times, choosing different pages and different text each time. Or move to edit-pdf, where text blocks are placed one at a time wherever you want them.

The pages are not redrawn: the note is laid over the real page, so the document's text stays text and the links go on working.

The page selection is strict: a number past the end of the document stops the whole job rather than being ignored. A document under an open password will not process either, so the protection has to come off first.

How this differs from the neighbouring tools

Four tools do outwardly similar things, and confusing them is expensive.

add-watermark either tiles a line of text diagonally across the whole page or stamps it once at a chosen point. Its opacity is adjustable, its angle is not: the diagonal is fixed. It is about the document's status, "Copy" or "Draft", not about a remark on a paragraph.

sign-pdf adds a signature and writes the signer's name into the file's properties. A note writes nothing into the properties.

redact-pdf blacks out and genuinely removes content. A translucent sticker is no substitute: everything under it stays in place and comes out with a copy and paste.

compare-pdf finds the differences between two versions itself and highlights them. If the task is to show what changed, marking it by hand is unnecessary.