To edit it. EPUB ní XHTML tí a lè pàṣẹ̀ padà nínú zíp - àkọ́lé tí a fi pàṣẹ́ padà padà sí ìwọ̀n ojú-ìwé wònyí, eyi ní idì tí àwọn awáròyìn e-ìwé fẹ́ rẹ̀, which is optimised for reading rather than revising; a document format is what you need to make changes, add comments, run a word count or hand the manuscript to an editor.