The .afpub file extension is the native, proprietary file format used by Affinity Publisher, a professional desktop publishing software developed by Serif. This format is designed to store complex layout projects, including multi-page documents, high-resolution imagery, vector graphics, typography, and intricate text formatting. Unlike flat file formats such as PDF, an .afpub file maintains a non-destructive, layered structure that allows users to edit individual elements, adjust text frames, modify master pages, and manage linked assets even after the project has been saved and closed. It serves as the working container for brochures, magazines, books, and marketing materials. Because it is a proprietary format, it is optimized specifically for the Affinity suite's engine, ensuring that all effects, adjustments, and document settings are preserved perfectly between sessions. Users typically export these files to industry-standard formats like PDF or IDML when they need to share their work with print shops or users of other software, but the .afpub file remains the primary source of truth for the design process.