How to study with PDFs: methods that actually work

Updated 13 October 2026 · ChatPDF guides · 7 sources

AI can miss or misstate things. Summaries and answers from AI tools, ChatPDF included, can leave out important details or get them wrong. Check anything that matters against the document itself, especially legal, medical, financial and exam material.

Key points
  • Rereading and highlighting feel productive but rank among the least effective study techniques in a large review of learning research. 1
  • Testing yourself from memory beats rereading for long-term retention, even though rereading makes you feel more confident. 2
  • Spread your reviews over days and weeks; the longer you need to remember something, the longer the gaps between reviews can be. 3
  • Use a PDF as the source of questions, not as something to stare at: read once, then quiz yourself, check and fix the gaps.

Most course material now arrives as a PDF: lecture slides, textbook chapters, readings and past papers. The natural way to study it is to scroll through again and again, highlighting as you go. Learning research says that is one of the weakest ways to spend your time. The methods that work best are less comfortable: closing the document and trying to recall what it said, spreading those attempts out over days, and explaining ideas to yourself in your own words. This guide shows how to apply them to any PDF on an iPhone, with or without AI.

What the research says

A widely cited review by Dunlosky and colleagues rated ten common study techniques by the strength of the evidence behind them 1. Two came out with high utility: practice testing (any kind of low-stakes self-testing, from flashcards to practice questions) and distributed practice (spreading study over time instead of cramming). Highlighting and underlining, rereading and summarization were rated low utility. Elaborative interrogation (asking yourself why a fact is true) and self-explanation (explaining how a new idea connects to what you already know) landed in between.

The testing effect is easy to underestimate. In one classic experiment, students who read a passage and then tried to recall it remembered more two days and one week later than students who simply reread it, even though rereading won on a test given five minutes later and left students feeling more confident 2. That gap between feeling and reality explains why rereading is so popular: it feels fluent, and fluency is easily mistaken for learning.

Spacing works alongside testing. A large review of distributed-practice studies found that spreading reviews out improves long-term recall, and that the best gap between sessions grows with how long you need to keep the information 3. For an exam a month away, reviews a few days apart beat several sessions crammed into one evening.

A study routine for one PDF

  1. Preview (about five minutes). Skim the title, headings, bold terms, figures and the summary or conclusion. Write down three questions you expect the material to answer.
  2. Read once, actively. Read a section, then look away and say or write what it said. Mark only the passages you could not recall; a highlight is a pointer to something you need to learn, not the learning itself.
  3. Make retrieval material. Turn the key points into questions: flashcards for facts and terms, practice questions for concepts and problems.
  4. Explain the hard parts. For each difficult idea, write two or three sentences on why it is true or how it connects to something you already know. Notes in your own words are a good home for these.
  5. Quiz, check, fix. Answer from memory first, then open the PDF and check. Anything you missed goes into the next session.
  6. Space the sessions. Repeat the quiz after a day, then after a few days, then a week or two later.
Day 0 Day 1 Day 3 Day 7 Day 14 Before exam Read Quiz yourself from memory, check, fix gaps Gaps grow as recall gets easier. The exact days matter less than spreading reviews out.
An example review schedule: read once, then test yourself at growing intervals instead of rereading the night before.

Free tools on your iPhone

You do not need a special app for any of this. In the Preview app you can select and copy text from a PDF and highlight or underline passages 4. You can attach a PDF to a note in the Notes app and write your questions and explanations right next to it 5. On iPhone models that support Apple Intelligence, Writing Tools can summarize selected text or turn it into key points 6; if the option does not appear where you are reading, copy the text into a note first. Treat any summary as a map of what to learn: reading someone else's summary is still rereading.

Lecture slides need a slightly different approach because they are sparse by design; see how to study from lecture slide PDFs. If your PDF is a scan and you cannot select any text, start with getting selectable text from a scanned PDF.

Where ChatPDF helps

ChatPDF is an iPhone app that answers questions about a PDF you import. Its suggested prompts include "Quiz me with 5 questions" and "Make flashcards", which give you retrieval material quickly, and you can ask it to explain a passage you are stuck on. For whole-document requests like these it reads a broad sample of the document rather than every word, so questions can lean toward some sections and skip others. Answers can be wrong and carry no page references, so check each one against the PDF before you memorize it. Questions you write yourself still matter: writing them forces you to process the material, which is part of the benefit.

If your course has rules about AI tools, read them first; see using AI PDF tools for school without cheating.

Common questions

Is highlighting a waste of time?

Not entirely, but on its own it does little for memory, and research reviews rate it low utility. Use highlights to mark what to turn into questions, then test yourself on those parts. 1

How many times should I review a PDF?

There is no single magic number. Keep quizzing until you can answer correctly on a later day, and spread the sessions out; the longer you need to remember the material, the longer the gaps can be. 3

Is an AI summary enough to study from?

No. A summary tells you what to learn, but reading it is passive. AI summaries can also leave out or misstate points, so use them as a guide and test yourself on the original material. 1,7

Sources and further reading

  1. Dunlosky J, Rawson KA, Marsh EJ, Nathan MJ, Willingham DT (2013). Improving students’ learning with effective learning techniques. Psychological Science in the Public Interest 14(1):4–58. doi:10.1177/1529100612453266 (summary page by the Association for Psychological Science). psychologicalscience.org
  2. Roediger HL, Karpicke JD (2006). Test-enhanced learning: taking memory tests improves long-term retention. Psychological Science 17(3):249–255. doi:10.1111/j.1467-9280.2006.01693.x psychology.ecu.edu
  3. Cepeda NJ, Pashler H, Vul E, Wixted JT, Rohrer D (2006). Distributed practice in verbal recall tasks: a review and quantitative synthesis. Psychological Bulletin 132(3):354–380. doi:10.1037/0033-2909.132.3.354 doi.org
  4. Apple Support. Annotate a PDF or image in Preview on iPhone (iPhone User Guide). support.apple.com
  5. Apple Support. Work with PDFs in Notes on iPhone (iPhone User Guide). support.apple.com
  6. Apple Support. Use Writing Tools to write, improve, and summarize content on iPhone (iPhone User Guide). support.apple.com
  7. Tang L, Sun Z, Idnay B, et al. (2023). Evaluating large language models on medical evidence summarization. npj Digital Medicine 6:158. doi:10.1038/s41746-023-00896-7 nature.com
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