Annotate PDF

Six tools: highlight (drag across text — fills a translucent rectangle, default yellow), underline (drag across text — draws a coloured rule below), strikethrough (drag across text — draws a rule through the middle), comment (click anywhere — opens a prompt for text, then drops a comment marker), draw (freehand pen — drag to sketch a path), and arrow (drag from point A to point B — draws a coloured line with an arrowhead). Pick a tool from the toolbar, choose a colour, and place items page by page using the prev/next controls.

Annotations are visual markup laid over a page — highlights, notes, arrows pointing at things. Editing means changing the content of the page itself (adding new text, shapes, or images that look like part of the document). On imisspdf, Edit PDF gives you that overlay-style editing with text boxes, shapes, and embedded images. Annotate PDF is for review and feedback markup. Practically: use Annotate when you are reviewing a document somebody sent you; use Edit when you are producing or amending a document yourself.

In this tool: no, the annotations get flattened into the page content stream when you click Save annotated PDF — they become part of the page graphics and other PDF readers cannot hide, toggle, or delete them. This is intentional for review workflows where you want the markup to be permanent and visible to every reader. If you need re-editable markup (highlights another reviewer can later remove from Acrobat or Preview), open the original PDF in Adobe Acrobat, Apple Preview, or Foxit — those tools save true PDF annotation objects (the /Annot dictionary), which is a different feature.

No. The file is read into your browser using FileReader, opened locally by PDF.js for the on-screen preview, and then re-saved with annotations flattened in by pdf-lib — all in WebAssembly, inside your tab. The DevTools Network panel will show zero outbound POST requests carrying your file. This matters most because annotation often happens on the most-shared documents: contracts being reviewed, manuscripts being copy-edited, design specs being marked up.

Not directly. PDF.js refuses to render encrypted PDFs without the password, and pdf-lib refuses to save back into one. Use our Unlock PDF tool to decrypt first (your password stays in your browser), annotate here, then re-protect with Protect PDF if needed. For PDFs flagged as "no modifications allowed" but not actually encrypted, pdf-lib usually ignores those permission flags and lets you annotate anyway — but the result will no longer carry the original certifying signature, since that signature was tied to the unmodified content.

The Draw tool captures mouse and trackpad input directly, which works fine for short marks and arrows but can feel jittery for handwritten notes. On a tablet with a stylus (iPad with Apple Pencil, Surface, Wacom), the browser receives the same pointer events and the drawing follows reasonably well — quality depends on the browser's pointer-event latency. For polished handwriting (lecture notes, signed comments), dedicated stylus apps like GoodNotes or Notability handle smoothing and pressure sensitivity better than any browser tool. Then export to PDF and import here only if you also need extra markup.