PDF annotation is simply adding your thinking to a document while you read it. A highlight can mark a useful passage; a margin note can explain why it matters. The aim is not to make every page colourful, but to leave a trail you can use when you study again.
Start with one chapter or article. A small, repeatable routine is easier to learn than a complicated system of symbols and colours.
Keep an original and make a study copy
Save the original file somewhere you can find it again. Give your working copy a clear name containing the course and topic, especially if your lecturer supplies several versions.
Different apps store annotations differently. Before working through a long document, add a test mark, close the file and reopen it. Check that the mark is still there and that you know how to undo or delete it.
If the document contains sensitive information, follow your institution's rules about where it can be stored. Do not upload material to an external service merely because the app offers that option.
Check what kind of PDF you have
Try selecting a sentence. Some PDFs contain selectable text; others are scans of printed pages. That difference affects text search and certain highlighting tools.
Optical character recognition, usually called OCR, can add recognised text to a scan where the software supports it. It is useful, but you can still draw, circle or write notes on many scanned pages without it. You do not need to abandon a reading because text selection is unavailable.
Check important quotations against the visible page. Recognition can make mistakes, particularly with unusual type, formulas or a poor-quality scan. Keep the page number with any quotation you plan to use later.
Give each annotation a job
Begin with a small toolkit. Use highlights for passages you will want to locate again, text notes for explanations and questions, and freehand marks for diagrams or connections.
For instance, highlight a definition and add an example in your own words. Beside an argument, write a question about its evidence. On a diagram, circle the part you cannot yet explain rather than covering the whole image with marks.
You do not need every tool available. Learn how to select, erase and move a mark before experimenting with stamps or elaborate colour schemes. Comfort with a few controls is enough to start useful reading.
Choose a workflow you can actually use
Try your routine with a real course file before moving your entire reading list into an app. Check page navigation, writing comfort and whether the marks remain easy to read at ordinary zoom.
For an example of handwriting, highlighting and text annotation tools, explore annotating PDFs with Kilonotes. Whatever software you use, the purpose of the mark matters more than the appearance of the toolbar.
If you study on more than one device, test access on each. If offline reading matters, disconnect briefly and check what remains available. Establish the limits before relying on the setup in class or during travel.
Read for meaning before marking heavily
Preview the title, headings and conclusion to understand the document's structure. Then read a section before deciding what deserves emphasis.
There is no correct number of highlights per page. A dense explanation and a page of examples may need different treatment. The better test is whether the mark helps you answer a question or find an important point later.
If a whole paragraph seems essential, add a brief summary rather than highlighting every line. When you cannot summarise it, leave a question and return after reading further. Uncertainty is a useful thing to record.
Turn annotations into study prompts
At the end of a section, write a short account of the main idea without copying the text. Add two or three questions you should be able to answer later.
A prompt might ask you to explain a term, compare two views or work through an example. Close the document and attempt the answer, then reopen it to correct gaps. Research reviewed by Roediger and Karpicke supports self-testing as a way to strengthen later retention compared with additional reading alone.
Keep source references attached to your summaries. If you combine several readings on one revision page, record which document supports each point. That saves time when preparing an assignment.
Check sharing and recovery before you need them
Export a short annotated file and open it in a different viewer. Check that handwriting, highlights and page order appear correctly. Find out whether your export preserves editable notes or turns them into a fixed part of the page.
Make a recovery plan too. Know where the working file is stored and how you would retrieve it after losing a device. Syncing and exporting are useful, but neither should be assumed to solve every backup problem.
Build the habit with one reading: save a copy, annotate selectively, write a summary and test yourself. Once that feels straightforward, apply the same routine to the next file. Useful annotation is less about marking more and more about leaving yourself something worth revisiting.