The builder reads text and images from the PDF, detects the specifications and tells photos from technical drawings (line-art). You can correct everything below.
Pick a photo/visual from your computer, or the graphic key-visual generated by the tool. The cover always keeps the A4 proportions.
Images found in the PDF. Set each role: Photo (free use), Drawing (goes to the Mechanical page), or Hero. Drawings flow automatically into the last page.