It’s fairly common for a project to have many components, each one a different size. Maybe it’s a branding project with a logo, letterhead, business card, envelope, poster, t-shirt, and brochure. Maybe it’s a book jacket with 2 flaps, a spine, and back and front cover. One approach is to create a new InDesign document for every separate piece. I would certainly do that for multi-page files like brochures and books. For one-page items, though, you could use another approach: create different page sizes inside the same InDesign document. I'll show you 2 ways to accomplish this.