How to draw on a PDF with a pen or shapes

Drawing on a PDF works through the Comment menu in PDF by Zaweba, which has a freehand pen with an eraser, and shapes: rectangle, oval, line, arrow, cloud, polygon and connected lines. Everything you draw sits on the page as a comment, so it can be moved, restyled or deleted later. The app is free and runs offline on Windows.

Drawing is good for marking up plans, circling a problem in a photo, pointing at a figure, or signing off a sketch with a quick note.

Freehand pen and eraser

Pick the freehand drawing tool and draw with the mouse, or with a pen if your PC has one. The pen stays in hand until you press Esc, so you can make several strokes, such as a circle and a tick, without picking the tool again each time.

The eraser is for freehand strokes. Drag it across a stroke and it cuts the parts under its path, so you can tidy the end of a line without starting again.

Shapes, lines and arrows

Rectangle, oval, line, arrow and cloud are drawn by dragging. Drag from one corner to the other for a box or an oval; from start to end for a line or an arrow. Clouds are the wavy outlines people use on drawings to mark an area that has changed.

Polygon and connected lines work by clicking. Click each corner in turn, then double-click or press Enter to finish. That's the way to trace an irregular area on a plan, or draw a route made of straight lengths.

Styling what you draw

Each drawing has properties: colour, fill, opacity, line width, dashed or cloudy borders, and ten line endings for lines and arrows. A thick red outline with no fill draws attention without hiding what is inside. A light fill at low opacity shades an area while keeping the text readable. Arrow endings and other line endings let the same line become a pointer, a dimension or a plain divider.

Comment, Properties also lets you set the author and subject, which helps when several people are marking the same file.

Adding words to a drawing

A shape on its own can be unclear. Double-click it to open its pop-up and type a note, or add a Callout, which is a text box with a leader line and arrow to the point it's about. Together they turn a circle on a page into a clear instruction.

Keeping drawings useful

Draw as little as you need. One arrow and a short note usually say more than a page covered in scribbles.

Zoom in before drawing anything precise. Shapes drawn at a high zoom land where you meant them.

If you need sizes rather than sketches, use the measuring tools instead, which give distance, perimeter and area with a drawing scale.

All drawings are listed in the Comments panel, so you can filter by kind to find them, and you can flatten them into the page when the drawing is final. Until then, they stay editable.

PDF by Zaweba does this offline, so plans, contracts and private papers stay on your own computer while you mark them up.