Or you can download a suitable app on your phone to help you download your pictures into PDF file.
Why do you need to do this?
When you submit your work in PDF file, online marking can be done on it.
When do you do this?
If you have a hardcopy worksheet which requires you to submit work on Google classroom. You take photos of your worksheet, convert them to PDF file, then you submit.
Click "Unsubmit".
Make your changes and then
click "TURN IN" again when you are ready to submit.