How Compression Works Inside EPUB, DOCX, XLSX, and PPTX?
Last Updated: 10 September, 2026
How Compression Works Inside EPUB, DOCX, XLSX, and PPTX If you rename a .docx, .xlsx, .pptx, or .epub file to .zip and double-click it, something surprising happens: it doesn’t throw an error. Your operating system opens it as a folder packed with subdirectories, XML configuration files, styling sheets, fonts, and embedded images.
Modern document architectures abandoned monolithic binary blobs decades ago. In their place, industry standards—namely Open Packaging Conventions (OPC) for Microsoft Office and the Open Container Format (OCF) for EPUB—adopted a surprisingly elegant foundation: the humble ZIP archive.