- How do the highlights and notes get saved into the PDF?
- They are drawn into the page content itself — a translucent rectangle for a highlight, a filled box with text for a note. This is the same mechanism a printer uses, so the marks appear identically in Acrobat, Preview, Chrome, on paper, and in any screenshot. The trade-off is that they are not clickable annotation objects: you cannot select, edit or delete them later in a PDF reader. Keep your original file if you expect to revise the markup.
- Is this the same as commenting in Acrobat?
- Not quite. Acrobat writes a separate annotation layer that other Acrobat users can reply to, toggle off, or export as a comment list. This tool flattens the marks into the page. That is better when you want the recipient to see exactly what you saw regardless of their software, and worse when you want a back-and-forth review thread. Pick the flattened version for sharing a marked-up copy, and a full reader for collaborative review cycles.
- Does my file get uploaded anywhere?
- No. Pages are rendered with PDF.js and the marks are written with pdf-lib, both running in your browser tab. The document is read from your disk into memory and the annotated copy is written back out the same way. Nothing is transmitted, which matters for the contracts, medical letters and financial statements people most often need to mark up.
- Why does it refuse notes in Hindi, Chinese or emoji?
- The note text is drawn with a PDF built-in font, and those fonts use WinAnsi encoding — Latin-1 plus a small block of typographic punctuation. Devanagari, CJK, Cyrillic and emoji have no glyph there at all. Rather than stamping a row of question marks onto your page and calling it done, the tool checks first, names the characters it cannot draw, and leaves the file untouched. Highlights have no such limit; they work over text in any script.
- Can I annotate a scanned PDF?
- Yes. Highlights and notes sit on top of whatever is underneath, so a scan behaves exactly like a text PDF. There is no text layer needed because nothing is being matched or searched — you are drawing on the page image. If you want the result to be searchable afterwards, run it through OCR PDF first, then annotate.
- How do I highlight a specific sentence accurately?
- Switch to Highlight mode and drag a rectangle across the line. Pages are rendered at 1.5x, so a sentence is comfortably large enough to trace at normal zoom. If a highlight lands wrong, Undo last removes it and you can redraw. Nothing is written to the PDF until you press Apply, so every mark is reversible up to that point.
- Is there a limit on file size or page count?
- The tool imposes none. The practical ceiling is your device's memory, because every page is rendered to a canvas image up front so you can see what you are marking. A few hundred pages is fine on a normal laptop; a very large scanned document on a phone may be slow. Split the file first if you hit that.
- Does the annotated file still work everywhere?
- Yes. The output is an ordinary PDF with no encryption, no annotation layer and no viewer requirement — the marks are part of the page. Page count, page sizes, existing form fields and document metadata are carried through unchanged; the only difference from your original is the marks you drew.
