One of the most important advantages of EPUB over PDF is reflowable text: you can set the font size, typeface, line spacing, and margins that suit you, and the text reflows to fill the screen at those settings. PDF viewers only zoom the fixed page — EPUB readers render the text fresh at your chosen settings. This makes EPUB far more comfortable for long-form reading, especially for academic and professional documents converted from dense two-column PDFs.
This guide covers how to adjust font settings on the main e-reading platforms and which settings make the biggest difference for different types of reading.
| Platform | Font size range | Custom fonts | Line spacing | Margins | Bold weight |
|---|---|---|---|---|---|
| Kindle (Paperwhite / Scribe) | 1–14 steps | Sideload via USB | 3 options | 3 options | Yes |
| Kobo (all models) | pt size (fine control) | Yes (sideload TTF/OTF) | Fine control | Fine control | Yes |
| Apple Books (iOS/macOS) | Slider | Embedded EPUB fonts | Yes | Yes | Yes |
| Readwise Reader | Slider | No (web fonts) | Yes | Yes | No |
| Moon+ Reader (Android) | Fine control (pt) | Yes (system fonts) | Fine control | Fine control | Yes |
| Thorium Reader (desktop) | Slider | No | Yes | Yes | No |
PDFs are fixed-layout documents — the page dimensions, font positions, and text flow are locked at the time of creation. Changing font size in a PDF viewer just zooms the entire page, requiring you to scroll horizontally. EPUBs are reflowable — the text is stored as structured HTML, and the reading application renders it at whatever font size you set. When you increase font size in an EPUB reader, the text reflows to fit the screen at the new size, just like a webpage adjusting to a browser window.
Comfortable font size is personal, but a good starting point is size 3–4 on the Kindle scale (out of 14 on newer Paperwhites). Academic text with dense information often reads better at size 2–3 to show more context per page; fiction and general non-fiction are comfortable at 3–5. Enable Bold font weight to increase contrast without increasing size — this is particularly helpful for Kindle displays in bright light.
Kindle supports a limited set of built-in fonts (Bookerly, Amazon Ember, Georgia, Caecilia, Palatino, Helvetica, Futura, OpenDyslexic) and custom fonts embedded in the EPUB itself. Kobo supports all built-in Kobo fonts plus any fonts you sideload — copy TTF or OTF font files to the fonts/ folder on the Kobo drive, and they appear in the font picker. Apple Books similarly supports embedded EPUB fonts and lets you choose from its built-in font library.
No — and this is intentional. When toolkit.bot converts a PDF to EPUB, it extracts the text content and creates a clean reflowable EPUB with a standard font stack. The original PDF fonts are not embedded in the EPUB because reflowable documents are designed to use the reader's chosen font. This lets you choose whichever font is most comfortable for you — including OpenDyslexic for dyslexic readers or a large, high-contrast font for low-vision readers.
The three settings that make the most difference are: (1) Font size — increase enough that you are not straining but not so large that pages turn too frequently; (2) Line spacing — increase to 1.5× or 2× for dense academic text to reduce eye fatigue; (3) Margins — wider margins reduce the line length and improve readability for long paragraphs. On Kobo, the Typography menu gives precise control over all three. On Kindle, the Reading Settings menu offers similar options. On Apple Books, the Aa button controls all these settings.
Related: EPUB dark mode guide · EPUB settings for dyslexia · Reading PDFs on Kindle