How to write on a PDF file

What is Adobe Acrobat Reader?

Adobe Acrobat Reader is the standard tool for reading PDF files (such as the files distributed in UKLO competitions). (Btw, PDF stands for ‘portable document format’.) It’s free, and if you haven’t already got it on your computer or your phone you can download it here. There is a paid version (Adobe Acrobat Pro) but you may never need it, and certainly won’t need it for the UKLO competition.

The free Reader allows you to do a lot of things with a PDF file:

  • to read it
  • to make marks on it
  • to fill in boxes on it.

For example, here’s a problem from 2020 which you can process like any of the 2021 problems. You can download it and practise on it. The picture below shows what you’ll see when you open it, including a few blue boxes where a user has entered

  • possible answers in the blue boxes
  • blue and orange marks on parts of the data, like the marks you might write on the data if you were using felt-tipped pens on a piece of paper.

The paragraphs below will explain how to do these things: how to add text in writable boxes, and how to draw marks on the data.

How to open a PDF document in Reader

If you’ve got Reader on your computer or your phone and you’ve downloaded a PDF file such as the one for the 2020 problem, you may be able to simply double-click the name of the file in order to open it in Reader. Otherwise you may need to right-click the file name and select Reader as the relevant app; how you do this will depend on your machine and its software, but in Windows 10 you select ‘Open with’ and then ‘Adobe Acrobat Reader’, and in Android you browse to the file in your browser, click it and choose ‘Adobe Acrobat Reader’.

How to fill forms

Once you’ve opened the file in Reader, if you’re using a computer you should see this at the top of the screen:

The most important icons for you are the two that are circled in the middle of the second row: the arrow and the hand. Make sure you click on the arrow (the only change will be in the shape of your cursor); the arrow selects a place in the document, while the hand is for moving around in the document, which you probably won’t need. On a phone, you won’t need to make this choice.

If you want to enter an answer in one of the boxes (like the C and B in the upper diagram), just select the box. Its colour will change to white, and you’ll be able to type into the box (using the keyboard that will have appeared on your phone).

How to make marks on a page

Suppose you’re working through the data. If you were working on paper you might well use a pencil or pen – or better still, felt-tipped pens of different colours. Using a computer, you can achieve the same effect with Reader as follows (but unfortunately this kind of editing doesn’t seem to be available on a phone):

  • Click the arrow next to the hand.
  • Click the little highlighter icon (the second from the left on the bottom row). As soon as you select this, you’ll see a large red circle appear at the other end of the tool bar. This allows you to change the colour of the highlighter.
  • Click the red circle and picking a colour.
  • Select a bit of text – a whole word or part of a word. This adds your selected colour to the background of the selected bit of text.
  • Move on to another bit of text.
  • At any point you can undo your last move by hitting Control + z on your keyboard.

Your browser

If you use your browser to navigate to a PDF file, it will open in the browser just like a web page. Try it with the sample UKLO problem. We’ve checked three popular browsers (Microsoft Edge, Google Chrome and Mozilla Firefox) and found that they all allow you to fill forms (with writable blank spaces, like our sample problem) in the PDF, and then to save the changed PDF file to your computer. So in this respect they’re a good alternative to the Adobe Acrobat Reader. But only one browser (Edge) allows you to add marks to the PDF, as Reader does, and even Edge doesn’t do this on a phone. So it looks as though Edge is a good alternative to Adobe Acrobat Reader for computer-users.

Here’s how to use each of the browsers to edit a UKLO problem after navigating to it and opening it in the browser. The following instructions apply to a computer; if you’re using a phone you may have to tweak the instructions.


  1. Computer: Click on any box to write into it using your keyboard; correct with the back-delete button.
  2. Phone: Open the file by clicking the Adobe icon (a sort of triangle in a red box), then click on any box to write into it; correct with the back-delete button.
  3. Computer only: To highlight text, click ‘Highlight’ in the top menu, select a colour, then select the relevant bit of text. This should add a little coloured box of colour round the highlighted text. If you make a mistake, you can erase it using the ‘erase’ tool on the top tool bar.
  4. Computer only: To draw on the document by adding a line, click ‘Draw’ and select a colour. Then drag your cursor where you want the line to appear.
  5. Computer: To save the edited PDF to your computer, click the little save icon (a ‘floppy disk’) in the top right and select the place on your computer where you want to store the file, then click ‘save’.
  6. Phone (Android): To save the edited PDF, hit the three dots (top right) and select ‘Save a copy’, then ‘Document cloud’, then choose a name.
  7. And to send the edited file back to your teacher, do what you would normally do.


Chrome is similar to Edge except that it doesn’t allow steps 2-4. To download you need to click the download arrow in the top bar, but if you can’t see it, just swipe across the page and it will appear.


Firefox is like Chrome except that the download button has a different icon (a down arrow on top of a floppy disk).