EPUB is a ebook format: it packages HTML, CSS, and images in a zipped OPS container as an ISO-standardised ebook format that reflows text to fit any screen width. XLSX is a spreadsheet format that stores cell values, formulas, formatting, and charts as zipped XML, the default format for Microsoft Excel 2007 and later. This conversion changes the file's encoding, compression method, and supported feature set. Metadata such as creation date and embedded colour profiles is preserved where the target format supports it. Converting between these two formats is common when the source application does not support XLSX natively or when the target platform only accepts XLSX. 1converter processes this conversion server-side using open-source tools. Files are transferred over HTTPS, converted on secure cloud servers, and automatically deleted after 24 hours.