Draw, highlight text, draw shapes, and add text comments onto any PDF file online for free with our PDF Annotator tool. Vector path compiler compiles all screen markups into sharp, valid PDF vector streams directly inside client browser RAM.
Load your PDF document into the interactive canvas annotation workspace.
Draw freehand lines, add text notes, highlight key sentences, and place shapes on any page.
Click Save Annotations to merge markup graphics into the PDF file and download.
Draw freehand lines, highlight document text, draw bounding box shapes, or type comments onto any PDF page.
Converts canvas coordinate points into native PDF SVG path commands, maintaining crisp vector graphics at any zoom.
All canvas rendering and PDF stream modification execute inside client browser memory. Zero files leave your device.
Interactive document annotation relies on a dual-layer HTML5 Canvas architecture. PDF.js renders background PDF vector pages to an underlying render canvas, while an overlay drawing canvas captures mouse and touch gestures (pen paths, shapes, text entries) stored as coordinate arrays.
Upon exporting, canvas coordinate points are scaled to match PDF page coordinate systems (x_pdf = x_canvas * (Width_pdf / Width_canvas)). Path points are converted into SVG path strings (M x y L x y...) and compiled directly into PDF page stream content using page.drawSvgPath().
By generating true vector paths rather than baking low-resolution raster images, annotations maintain high resolution, crisp lines, and lightweight PDF file sizes with 100% browser-based privacy.