PDF is a document format: it stores fixed-layout pages with embedded fonts, vector graphics, and page geometry defined by ISO 32000. EPUB is a ebook format that packages HTML, CSS, and images in a zipped OPS container as an ISO-standardised ebook format that reflows text to fit any screen width. This reformats the fixed-layout document into a reflowable ebook that adapts to screen size. 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 EPUB natively or when the target platform only accepts EPUB. 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.