Each sheet has forty numbered points around the outline of a picture and the details already drawn inside it. Joining the numbers closes the shape, and the finished page is then a coloring page.
The dots follow the outline of the whole figure rather than one part of it. A snowman is three balls, a hat and two arms fused into one silhouette, and that fused edge is what the numbers run around.
Not every drawing makes a good one. A shape has to have an outline worth joining, so the snowflake -- thirty-six spurs and no readable edge -- has a coloring page and a colour by number but no dot to dot.
Numbers are set as outlines rather than as text in a font, so a printed sheet looks the same everywhere and the PDF carries no font at all.