Apple Books keeps every highlight you make and never asks you about one again. Here are three ways to get highlights from an EPUB, PDF or Kindle book into a spaced-repetition deck on iPhone or iPad: the manual Anki route, a paid sync service, and a reader that skips the export entirely.
Case #006 — TL;DR
Manual route: share your notes out of Apple Books, reshape them into 'front;back' lines on a computer, and import them into Anki. On iPhone that means AnkiMobile, a one-time $24.99 in the US, or the free AnkiWeb site in Safari.
Paid route: Readwise or a similar service gathers Kindle and app highlights in the cloud and resurfaces them or pushes them to Anki. Reliable, but a subscription, and for Kindle purchases it is the only route.
No-export route: use a reader where a highlight already is a card. GemReader is a free EPUB and PDF reader for iPhone and iPad with a spaced-repetition Study tab built in. Existing Anki decks (.apkg / .txt) import into the same queue, so you don't need AnkiMobile for them.
Kindle Store books carry DRM that no third-party reader can open, so for those the paid route is the only option.
Verdict
If your books are EPUB or PDF, skip the export. The export step is where most people quit, and a reader with review built in removes it. If your library is Kindle purchases, a highlight-sync service is the only path that doesn't involve retyping.
Why highlighting alone doesn't stick
Highlighting barely helps retention on its own. Retrieval practice, where you're asked the question and have to produce the answer, is one of the strongest study techniques measured. A highlight is a bookmark for a question you never get asked.
Spaced repetition closes that gap by asking again at growing intervals. The method isn't the problem. The problem is the pipeline from 'I marked this sentence' to 'this sentence is a card I'll see next Tuesday', and every step in it is a place to quit.
Method 1: Apple Books to Anki, by hand
In Apple Books, open the book's list of highlights and notes from the contents menu, select the ones you want, and share them to Mail or Notes. Kindle on iPhone has a notebook of your annotations too, though publishers cap how much of a purchased book can be exported.
On a computer, reshape each highlight into one line with a separator between question and answer. For a definition, that usually means splitting the sentence at 'is' or 'means'. Save it as a semicolon- or tab-separated text file and import it into desktop Anki.
Getting the deck back onto the phone costs money or convenience. AnkiMobile is a one-time $24.99 in the US (the Android version is free). The free alternative is syncing to AnkiWeb and reviewing in Safari. Either way the deck is a snapshot: new highlights need another export, and edits in the reader never reach it.
Method 2: A highlight-sync service
Readwise is the best known. It connects to your Kindle account, takes exports from other apps, resurfaces a few highlights a day, and can push them into Anki. Competitors do a similar job at different prices.
It is the right answer for Kindle purchases, which nothing else on iPhone can open. The trade-offs are a monthly fee for what is mostly a text mover, your reading data on someone else's server, and, unless you set up the Anki push, a review that shows you highlights instead of testing you on them.
Method 3: A reader with review built in
The shortest pipeline is no pipeline. In GemReader on iPhone or iPad, select a passage, pick one of six colours and optionally type a note. It is now a card in the Study tab with the scheduler attached. The highlight is the front, your note is the back, and the book and location travel with it, so the card never loses its context.
Highlights and notes take tags, and the Study tab drills by book, by tag or across the whole library. Got Anki decks already? Import the .apkg or .txt file and they share the queue with your own highlights, so one session covers both.
Nothing leaves the device. There is no account and no server, and the library and the deck live in the same encrypted database. That also means it only helps with books the app can open: EPUB, PDF, MOBI and DRM-free AZW3. The free Book Checker tells you in Safari whether a file is locked, without uploading it.
Lecture PDFs and scanned handouts
PDFs highlight the same way EPUBs do, as long as the file has a text layer. A scanned handout is a stack of images with no text to select, so there is nothing to highlight. Run it through a scanner app or desktop PDF tool that does text recognition (OCR), then re-import it. The PDF Text Layer Checker tells you which kind you have.
Cards worth reviewing
Whatever the pipeline, the cards decide whether it works. Highlight the claim, not the paragraph; a card that takes thirty seconds to read gets skipped. Put a question in the note. 'Why does X fail under Y?' on the back of the passage that explains it turns a re-read into a retrieval prompt.
Use colours as categories you'll filter by later, such as definitions, examples or points you disagree with, not as an intensity scale. And expect to delete. A deck full of cards you always get right is a deck you stop opening.
Studying on Android as well? The Android version of this guide covers AnkiDroid and the readers there.
Start with the book you're reading now
GemReader is free, has no ads and needs no account. Textbooks, lecture PDFs and workbooks live in one library on your iPhone or iPad. Highlight as you read, then study those highlights as flashcards, without exporting anything or leaving the app. Download it free, import an EPUB, and your first highlight is the first card in the deck.
Try it yourself