Highlight text in a PDF

A marker, not a text selector

Many PDF apps highlight by selecting text, letter by letter. Octoolo's highlight is a box you drag over any part of the page. That has upsides and a downside:

• It works everywhere: scanned pages, photos turned into pages, tables, charts, handwriting, even a stamp on a scanned letter.
• It covers a block at once: a whole paragraph or a row of figures in one drag.
• It does not follow lines of text. A sentence that wraps onto the next line needs two boxes, one per line.

The color is laid over the page with a multiply blend at a little under half strength, the way a real marker works: dark text stays dark and easy to read, and only the paper around it takes the color. Zoom in with Larger before marking small print, so the box sits neatly on the line.

Colors with a purpose

Five marker colors are ready: yellow, mint green, light blue, pink and orange. The color button beside them picks any other, and a highlight's color can be changed later by selecting it.

A simple system helps anyone reading after you: yellow for key points, green for what is agreed or correct, pink for problems and questions, blue for names, dates and amounts. In a contract, mark the clauses to discuss in one color and the figures to check in another, then explain the code in a short note at the top of the first page with Text.

Light colors keep dark text easy to read. A very dark custom color makes the words under it hard to make out, even with the blend. Orange or pink on the signature lines of a long document is a handy reminder of where a signature is still missing.

How highlights are saved

Highlights are drawn into the page when you save. Every PDF reader shows them, and they print as they look on screen: in color on a color printer, as light gray on a black-and-white one.

Because they are part of the page, they are not PDF comments. They do not show up in a reader's comments list, and the person you send the file to cannot delete them with one click. Keep the unmarked original if you will need a clean copy later.

Until you save, every highlight stays editable, and Ctrl Z undoes the last one. The page bar puts a small dot on pages that have something added, so in a long document the marked pages are easy to find again. Your work is also kept as you go, so a closed window does not cost you an evening of reading notes.

Who highlights PDFs, and why

• Students marking up readings, articles and past papers.
• Anyone reviewing a contract or lease before signing it, then signing it in the same window.
• People checking statements and invoices, who highlight the charges they are asking about and send the page back.
• Colleagues writing a how-to, pointing at a button in a screenshot turned into a PDF; see PNG to PDF.
• Researchers and editors marking quotes to cite, figures to verify or passages to cut.
• Job seekers marking the requirements in a job ad saved as PDF, to answer each one in a cover letter.

Since the PDF never leaves your computer, highlighting a medical letter, a payslip or a legal document does not mean sending it to a website first.