Word to EPUB

Both formats are zip files. Rename either one to .zip, open it, and you find XML. The naive conversion (pull the paragraphs out of one, wrap them in tags, put them in the other) takes an afternoon to write, which is why there are two hundred sites offering it and why their output is recognisable at a glance.

What follows is the distance between that and a file worth selling, step by step.

1. Undo Word’s run splitting

Word stores text in runs: stretches that share formatting. In theory one italicised phrase is one run. In practice Word splits a run at every spell-check boundary, every language detection, every revision save, so the word “lighthouse” in italics routinely arrives as three runs.

Emit one element per run and you get <em>light</em><em>ho</em><em>use</em>. Many reading systems render that with hairline gaps, and all of them handle it worse than a single element. The first thing any serious reader of DOCX does is coalesce adjacent runs with identical formatting, and before building any tree, because afterwards the information needed to compare them is gone.

2. Know which parts of the file are lies

Several things in a DOCX look like content and are not. Reading them is how a converter puts nonsense in a book.

3. Find the chapters

An EPUB is a sequence of documents. A manuscript is one long flow. Splitting it is the step that decides whether the result is a book, and there are three kinds of manuscript in the world:

• The author used Heading 1. The easy case, and the only one most converters handle. One detail even here: match on the style’s name, not its id. A French Word writes w:styleId="Titre1" and a German one writes Überschrift1; both carry w:name="heading 1". Matching the id works on English documents and silently flattens everyone else’s chapters into body text.
• The author pressed Ctrl+Enter between chapters and typed the titles in bold, centred, 16pt. This is the most common manuscript there is. Word knows nothing about it, since every paragraph is styled Normal. Split on the page breaks, then look at the first line of each piece to see whether it is a title and promote it if so, because otherwise the printed book carries every chapter title twice.
• Neither. A continuous flow with lines reading “Chapter Seven”. Scan for them, and tell the author that is what you did.

4. Fix the typography

A manuscript is typed. A book is set. The differences are small individually and cumulative in effect:

• Straight quotes become typographic ones, and contextually, so that ’tis and the ’90s get an apostrophe rather than an opening quote. The hard part is doing it across formatting boundaries: the apostrophe in <em>don</em>’t has its antecedent in a different element.
• Double hyphens become em dashes, three dots become an ellipsis.
• The double space after a full stop goes. It is a typewriter convention for monospaced type and it leaves holes in a proportional face.
• Tabs at the head of a paragraph go. Indentation is a typographic decision, not text.
• A paragraph containing only * * * becomes a scene break, with the glyph decided by the design rather than left as three literal asterisks.

5. Build a package that validates

An EPUB 3 is not “some XHTML in a zip”. Five things are required and all five are what generic converters get wrong:

And three things that are not required, and matter

• Landmarks. They are what a reading system’s “go to the beginning” uses. Without them, the book opens on the cover or the copyright page and every reader starts by swiping past the front matter.
• Semantic sections. An epub:type and a matching ARIA role on each section is what distinguishes a chapter from a copyright page, for a reading system and for a screen reader.
• Accessibility metadata. Since June 2025 this is close to mandatory for ebooks sold in the EU. See accessible EPUB.

6. Write a stylesheet that gets out of the way

The hardest thing to accept about ebook CSS is how little of it there should be. Three rules account for most bad EPUBs:

• Never set a font size in points or pixels. The reader chose a size, on a device you have never seen, sometimes for their eyesight. Overriding it is the single most damaging thing an ebook stylesheet can do.
• Never set a text colour or a background. A book that specifies color: #000 is unreadable in night mode: the reading system darkens the background and the author’s black text stays black.
• Never set margins on the body. The reading system owns the page margins. Adding more produces a text block that shrinks every time the reader widens theirs.

What a stylesheet should do is set the relationships: the indent, which paragraphs are exempt from it, the space around a block quote, what a scene break looks like, all in units that scale with whatever the reader picked. That is the whole of good ebook CSS and it fits on a page.