PDF and EPUB answer fundamentally different questions about how a document should exist in the world. PDF asks: 'How should this look on a specific page size?' EPUB asks: 'How should this content be presented on any screen?'
PDF fixes content to a page. A 6"×9" PDF looks fine printed and on a large monitor, but on a 4-inch phone screen it requires pinching and panning to read. EPUB has no fixed page — its text reflows to fill whatever screen it's on, adjusting line breaks, font size, and margins to the reader's preferences. This is what every e-reader, Kindle, and reading app expects from ebooks.
Neither is universally better. Academic papers typically circulate as PDF because their tables, equations, and figures have precise spatial relationships. Novels, textbooks intended for e-readers, and business books use EPUB because people read them on devices of many sizes.
How PDF and EPUB Work
PDF: Fixed Page Layout
PDF (Portable Document Format, ISO 32000) was designed to represent printed pages in digital form. Every element on every page has absolute coordinates — it's essentially a digital print job. This makes PDF perfect for documents where layout is meaning: a balance sheet where columns must align, a map where annotations must sit at precise locations, or a magazine where text wraps around specific images.
The fixed-page design is also PDF's limitation for reading. On a small screen, a standard 8.5"×11" PDF page must be read by zooming and scrolling — or the text is too small to read without zooming. Some PDF readers have a 'reflow' feature that extracts text and reflows it, but this breaks tables, equations, multi-column layouts, and captions. Complex PDF layouts can't be meaningfully reflowed.
EPUB: Reflowable Web-Based Content
EPUB (Electronic Publication, maintained by the W3C/IDPF) is essentially a ZIP archive containing HTML, CSS, images, and metadata. The content is structured like a website — semantic HTML with CSS styling — and the reading app renders it on whatever screen it has. The reader can change font size, font family, line spacing, margins, and screen brightness. The same EPUB that fills a 13-inch tablet screen with large text fills a 5-inch phone with normal text and reflows automatically.
EPUB 3 (the current version) supports embedded audio, video, JavaScript interactivity, MathML for equations, and SVG for graphics. EPUB 3 is the format used by all major ebook retailers and reading apps: Kindle (via KFX conversion internally), Apple Books, Google Play Books, Kobo, and library systems like OverDrive.
Technical Comparison: PDF vs EPUB
| Feature | EPUB | |
|---|---|---|
| Layout type | Fixed (page coordinates) | Reflowable (adapts to screen) |
| Underlying technology | ISO 32000 page description | HTML5 + CSS3 in ZIP container |
| Font resizing by reader | No (text size fixed) | Yes (reader-controlled) |
| Font family choice | No | Yes (reader-controlled) |
| Screen size adaptation | No (pinch-zoom required) | Yes (reflows automatically) |
| Multi-column layout | Excellent | Limited (unreliable across readers) |
| Tables | Excellent (exact placement) | Good (but may scroll horizontally on small screens) |
| Mathematical equations | Excellent (PostScript rendering) | Good (MathML in EPUB 3; older readers vary) |
| Print output | Exact (designed for printing) | Variable (pagination depends on reader settings) |
| DRM | Password encryption; Adobe DRM | Adobe DRM (ADEPT); Kindle DRM; LCP |
| Accessibility (screen reader) | Good (if properly tagged) | Good (semantic HTML structure) |
| Annotations | Native (Acrobat Reader, most viewers) | Native in most reading apps |
| Audio/video embedding | Limited | Native (EPUB 3) |
Reading Experience by Device
| Device / App | EPUB | |
|---|---|---|
| Desktop (large screen) | Excellent — pages display at full size | Good — but fonts may feel oversized; better for text |
| Tablet (10"+ screen) | Good — pages fit with room for annotations | Excellent — ideal reading size |
| Phone (5-6" screen) | Poor — constant pinching and scrolling | Excellent — text reflows to perfect size |
| Kindle e-reader | Poor — fixed layout with limited reflow | Excellent (Kindle converts EPUB to KFX internally) |
| Kobo e-reader | Acceptable (small screen issues) | Excellent (native EPUB support) |
| Apple Books (iOS) | Good (iPad); Poor (iPhone) | Excellent (preferred format) |
| Google Play Books | Accepted but limited | Native format |
| Browser (Chrome, Firefox) | Native viewing | Requires extension or conversion |
File Size Comparison
EPUB files are typically smaller than equivalent PDF files for text-heavy content because EPUB stores text as HTML (highly compressible) while PDF embeds fonts. For image-heavy content, sizes may be similar.
| Content Type | EPUB | |
|---|---|---|
| 300-page novel (text only) | 1-3 MB | 300-600 KB |
| 300-page textbook (text + images) | 20-80 MB | 10-30 MB |
| Academic paper (10 pages) | 300-800 KB | 100-300 KB |
| Illustrated children's book (40 pages) | 10-30 MB | 8-25 MB |
Use Case Decision Matrix
| Use Case | Best Format | Why |
|---|---|---|
| Novel / narrative nonfiction | EPUB | Long text; readers want font control on phones/e-readers |
| Business book for Kindle | EPUB | Amazon converts EPUB to their format; optimized for devices |
| Academic paper | Multi-column, equations, figures with precise captions | |
| Technical reference manual | Tables, code blocks, cross-references require fixed layout | |
| Textbook (print edition) | Must match print layout exactly for page references | |
| Textbook (digital-only edition) | EPUB | Students read on laptops and phones; reflowable preferred |
| Recipe book (print-style) | Visual layout important; reader wants photos alongside steps | |
| Self-published ebook for stores | EPUB | Required or preferred by Apple Books, Kobo, Google Play |
| Company report / annual review | Brand identity, precise layout, print-ready | |
| Library e-lending | EPUB | OverDrive, Libby, and library systems use EPUB with LCP DRM |
When to Use PDF vs EPUB
Use PDF When...
- Layout is part of the meaning — Academic papers, reports, manuals, legal documents where spatial relationships between content matter
- Print compatibility is required — Anything designed to be printed as well as read digitally
- Tables and figures have complex relationships — PDF preserves the exact visual position of captions, footnotes, and annotations
- Wide software compatibility for viewing — PDF opens in every browser natively; EPUB requires a dedicated app
- Official/archival documents — PDF/A is the international archive standard; EPUB has no archival standardization equivalent
Use EPUB When...
- Creating ebooks for commercial platforms — Apple Books, Kobo, Google Play Books all require or strongly prefer EPUB
- Primarily text-based content — Novels, essays, narrative nonfiction benefit enormously from EPUB's reflowable layout
- Readers will use phones and e-readers — EPUB is the only format that provides a genuine reading experience on small screens
- Accessibility matters — EPUB's semantic HTML structure is better for screen readers than PDF, though both can be made accessible with effort
- The document will be updated — Updating an EPUB (just HTML/CSS) is easier than a precisely laid-out PDF
Convert PDF to EPUB (or EPUB to PDF) with ChangeThisFile
ChangeThisFile supports PDF ↔ EPUB conversion via /pdf-to-epub and /epub-to-pdf. PDF to EPUB conversion extracts text and restructures it as reflowable HTML — complex multi-column layouts with tables and equations may lose fidelity. EPUB to PDF conversion via Calibre produces print-ready output.
curl -X POST https://changethisfile.com/v1/convert \
-H "Authorization: Bearer YOUR_API_KEY" \
-F "file=@ebook.epub" \
-F "target=pdf" \
-o ebook.pdf690 routes supported. Free for 1,000 conversions/month.