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Annotate PDF
Comment, highlight and draw. Free, no sign-up.
How to annotate PDF
Annotations are written into the PDF so any reader can see them.
- Open your PDF. It loads straight into the editor.
- Mark it up. Highlight, draw, or drop a comment anywhere.
- Download. Your notes are saved into the file.
What a highlight becomes in the file
Every mark is drawn into the page's own content, using the same kind of instructions that put the document's text and rules there. A highlight is a tinted rectangle over each line box your selection covered; underline is a rule near the foot of the line and strike a rule through the middle; the pen is a run of round-capped segments following your hand; the box is a thin outline; a note is real vector text at 13 point in the swatch colour you chose. Nothing is turned into a picture and the page's own text is left alone, so the document stays selectable, searchable and sharp at any zoom, and every reader draws the marks identically.
The same fact cuts the other way. Once the file is downloaded the marks are part of the page, so you cannot come back later and move or remove one. Fix things before you download — Erase drags across the page and takes out each whole mark it touches, including a highlight that ran over four lines — and keep your original. If what you want is a remark someone can reply to, resolve or delete afterwards, that is Comment & review, which writes separate annotation objects instead.
Highlighting needs a text layer
Highlight, underline and strike are built from the selection your browser makes over the rendered text layer, which is what makes them snap to the real lines: a selection running across three lines becomes three neat marks rather than one crude block. A scanned page has no text layer to select, so dragging picks up nothing and those three tools appear to do nothing at all. That is the commonest "it isn't working" on this page, and the fix is OCR PDF — recognise the scan first and highlighting behaves normally afterwards.
The pen and the box need no text at all, since they take their coordinates from the page. They are also the right choice on a document whose text layer is scrambled: some PDFs store characters in a different order from the one they display, which makes a selection jump around the page. Draw on those rather than fighting them.
Questions
Will other PDF readers show my highlights?
Yes. They are standard PDF annotations, not a private layer, so Acrobat, Preview and browser viewers all display them.
Does a highlight make the text underneath harder to read or copy?
No. Highlights are drawn at 40% opacity in multiply blend, which tints the paper rather than washing over the ink, so the words stay black and legible. The text itself is untouched, so it still selects, copies and searches exactly as before.
Can I write a note in Arabic, Korean or Thai?
Yes. Notes are drawn with the bundled font set, with proper shaping and right-to-left ordering, so Arabic joins up and Thai marks sit where they belong instead of coming out as empty boxes.
Can I annotate a password-protected PDF?
Not directly. The editor tells you the file is protected and stops there. Remove the password with Unlock PDF first — you need the password — mark up the unlocked copy, and protect it again afterwards if it matters.
Are my files uploaded to a server?
No. Every tool on this site runs inside your browser, using the same engine as the Folia desktop app. Your file is read from your disk into your browser’s memory, processed there, and handed back as a download. It never crosses the internet, so there is nothing for us to store, leak or hand over.
Is there a file size limit?
We impose none. The only ceiling is your own device’s memory, which differs from one computer to another — so we read what your browser reports about this machine and show the resulting limit on the page. Light tools like merge and rotate handle far more than heavy ones like OCR, which must render every page. For anything larger, Folia for Desktop has no limit at all.
Is it really free? Do I need an account?
Yes, and no. Every tool is free and unlimited, with no watermark and no sign-up. Ads pay for the site, and your own computer does the work, which costs us nothing. Signing in with a paid Folia plan simply removes the ads.