With ToolBook software, users may transform e-books in its own format (.spb) to Adobe PDF (Portable Document Format) files, hence essentially achieve spb to pdf conversion - the only possible one we know of.
ToolBook is available only for Windows, but you can use a virtualization software tool on Mac or Linux computers to launch the program in virtualized environment so you can convert spb to pdf.
Updated: June 15, 2023