When the Built-In Fonts Are Not Enough: Loading Your Own
Most readers never need a font that did not ship with the app. The bundled set covers Latin text with a serif, a sans, and something for dyslexia, and that is the choice most people want.
The people who do need more are not being fussy. They are reading in a script the bundled fonts render badly, and the difference is not taste — it is whether the letters are correct.
Where bundled fonts fall short
Devanagari builds conjunct consonants by combining glyphs. A font without the right ligatures renders them as separate letters with visible half-forms, which is legible in the way a misspelling is legible.
Thai stacks marks above and below the base line. Fonts that were not designed for it collide the marks with the letters above, and long vowels drift.
Arabic joins letters differently depending on position in the word. A font missing the contextual forms produces disconnected letters, which reads roughly the way English would if every word were spelled with spaces between the letters.
CJK is a size problem rather than a shape one. A font missing a character shows a replacement box, and the set of characters a Japanese or Chinese book might use is very large.
Screenshots of these problems get reported as app bugs. They are font coverage problems, and the fix is a font.
Adding one
Aurora Reader accepts .ttf and .otf files. Pick the file from storage and it becomes available in the reading settings alongside the bundled faces.
Two practical notes. Variable fonts in a single .ttf usually load at their default weight rather than exposing the whole range, so if you want a lighter or heavier cut, install that cut as its own file. And a font file only helps if it actually contains your script — a beautiful Latin serif added for a Hindi book will simply fall back for every Devanagari character, which looks like nothing happening.
Fonts worth adding
For scripts the bundled set handles unevenly, the Noto family exists precisely for this: it was built to cover scripts systematically rather than to be distinctive, and it is free.
For Latin reading, the honest answer is that the bundled fonts are fine and the gains from swapping them are small. If you are chasing comfort rather than correctness, size, line spacing and margins will do more for you than any typeface will.
The one exception for Latin readers
If you find reading tiring in a way that font size does not fix, a font designed for the problem is worth trying — OpenDyslexic is bundled, and other options exist as downloads. Whether they help is genuinely individual, which is covered in the guide to dyslexia-friendly reading settings.
Try one for a whole chapter before deciding. First impressions of typefaces are mostly novelty, and novelty wears off in about ten minutes.
What a font cannot fix
If the characters are wrong rather than ugly — random symbols, question marks in boxes across the whole file — the problem is not the font but the encoding, and no font will help. That case is broken characters in a text file, and it is fixed by re-saving the file rather than by changing how it is displayed.