I’ve watched seasoned designers hit this wall. I’ve watched interns panic over it. Same confusion every time.

You have a finished InDesign file, Word document, or PDF and someone says:

“Great. Now export it as EPUB.”

And suddenly nothing works the way it should.

Text breaks. Images float into weird places. Chapters disappear. Or worse — the EPUB “works” but looks terrible on Kindle or Apple Books.

Here’s the truth nobody explains early enough:

EPUB is not a fixed layout format. It’s basically a mini website.

Think HTML + CSS inside a zipped file.

So when you convert DOCX, PDF, or InDesign, you’re not “saving as another file.”
You’re translating a visual layout into structured HTML.

That translation is where things break.

Let’s walk through how professionals actually handle it.

The #1 Thing That Breaks EPUB Conversions

This is the mistake I see constantly.

People format visually instead of structurally.

Meaning they do things like:

Increase font size instead of using Heading styles
Add spaces between paragraphs instead of paragraph spacing
Hit Enter five times to create a page break
Bold chapter titles manually

Looks fine in Word or InDesign.

But EPUB conversion tools depend on structure, not appearance.

The converter is asking:

What’s a chapter?
What’s a heading?
What’s body text?
Where do images belong?

If the document doesn’t answer those questions, the EPUB gets messy.

Fix this first before converting anything.

Converting Word (DOCX) to EPUB — The Reliable Method

Word is actually one of the easiest formats if the document is structured correctly.

But don’t export directly from Word unless the file is extremely clean.

Professionals usually run it through Calibre or Sigil.

Step 1 — Clean the Word File

Before conversion:

Make sure:

Heading 1 = chapter titles
Heading 2 = subheads
Body text uses Normal style
No manual font overrides everywhere
No empty paragraphs used for spacing
Images inserted inline, not floating

Quick check:

Open the Styles panel in Word.

If everything says Normal + Bold + Font Change + Weird Stuff you need to clean it.

Trust me. This saves hours later.

Step 2 — Export as DOCX (not PDF)

This matters.

Always convert from DOCX.

Never convert from PDF unless you absolutely must.

PDF destroys structure.

Step 3 — Convert Using Calibre

Calibre is the quiet hero of ebook publishing.

Open Calibre
Add your DOCX file
Click Convert Books

Choose EPUB.

Important settings:

Structure Detection → Chapter = Heading 1
Table of Contents → Heading 1

This tells Calibre where chapters begin.

Export.

Open the EPUB in Apple Books or Calibre Reader to preview.

Converting InDesign to EPUB (The Professional Route)

If the book was designed in InDesign, you’re already halfway there.

Adobe built EPUB export directly into the software.

But again — structure matters.

Before Exporting Anything

Open Paragraph Styles.

Every element should have a defined style:

Chapter title
Body text
Quote
Caption
Subhead

Never rely on manual formatting.

This is where most EPUB exports fail.

The Actual Export

Inside InDesign:

File → Export
Choose EPUB (Reflowable)

Not fixed layout unless it’s a children’s book or comic.

Reflowable is what Kindle and most ebooks use.

Key export settings:

Split Document → Paragraph Style: Chapter Title
Table of Contents Style
Preserve Local Overrides: OFF

Export.

Then test it.

Weird InDesign Edge Case (You’ll Eventually Hit This)

Images anchored incorrectly.

If images jump to strange locations in EPUB, check:

Are they anchored to text?
Are they floating on the page?

EPUB hates floating images.

Anchor every image to a paragraph.

Converting PDF to EPUB (The Hard Way)

Let me save you some pain.

PDF → EPUB is the worst conversion path.

Why?

PDF files are designed for printing, not structure.

A paragraph in PDF might actually be:

line 1 text block
line 2 text block
line 3 text block

Three separate objects.

Now imagine converting that to HTML.

It gets ugly fast.

When PDF Is the Only Source

Use Adobe Acrobat Export first.

PDF → Word (DOCX)

Then clean the DOCX.

Then convert to EPUB.

Yes. Two steps.

But it works far better.

The Tools Professionals Actually Use

You’ll see these constantly in publishing workflows.

Tool	What It Does	When To Use
Calibre	Converts many formats to EPUB	Best universal converter
Sigil	EPUB editor	Fix formatting after conversion
InDesign	Native EPUB export	Best for designed books
Pandoc	Advanced document conversion	Technical publishing
Vellum	Paid ebook creator	Indie author workflows

Most real workflows use two tools:

Convert → Edit → Validate.

The Simple Fix Everyone Misses

Here’s something beginners overlook constantly.

Always open the EPUB and inspect it before publishing.

An EPUB is just a zip file.

Rename it:

book.epub

book.zip

Open it.

Inside you’ll see:

HTML files
CSS
images
metadata

If something breaks in the ebook, you can often fix it right there.

Or use Sigil, which edits those files visually.

When EPUB Looks Perfect… Until You Upload It

This happens on Kindle Direct Publishing a lot.

Your EPUB looks fine locally.

Upload it.

Suddenly:

spacing changes
images shift
chapter breaks disappear

Why?

Retailers reprocess EPUB files.

Different engines:

Platform	Rendering Engine
Kindle	KindleGen
Apple Books	WebKit
Kobo	RMSDK

Each behaves slightly differently.

That’s why professional publishers test on multiple readers.

Quick Troubleshooting Checklist

If your EPUB looks broken, check these first:

No manual spacing between paragraphs
Images anchored inline
No empty paragraphs
Heading styles used properly
No text boxes in InDesign
No tables used for layout

Tables are another hidden EPUB killer.

Still Broken? Here’s the Nuclear Option

When conversions keep failing, do this.

Strip the formatting completely.

In Word:

Paste the entire manuscript into Notepad.

Yes. Really.

Now paste it back into Word.

You now have pure text.

Apply clean styles:

Heading 1 for chapters
Normal for body
Reinsert images

Then convert again.

Nine times out of ten, the EPUB suddenly works.

All the hidden formatting garbage is gone.

The One Thing I Wish Everyone Knew Before Starting

Don’t design ebooks like print books.

That instinct causes most problems.

Print design controls everything.

EPUB design controls almost nothing.

The reader controls:

font
font size
margins
line spacing
screen size

Your job isn’t layout.

Your job is clean structure.

Once that clicks, EPUB conversion becomes easy.

And once you’ve fixed your first messy conversion…
you’ll spot the problems instantly next time.