Some teachers may ask you to fill out PDF files as part of your assignment. This might especially be true in Math, where you need to write on the file in order to solve the problems.

If the files are assigned through Google Classroom, a tablet/iPad or phone is the best option to work with these. Install the app for Google Classroom. The app has a pencil at the top that lets you edit the file, save it, and turn it in with your edits included. 

If the files are not sent through Classroom, you'll need to use another program. One good one: PDF Escape. It works on computer browsers as well as tablets. Important things about this site:

1. Do not click any ads. The ads may try to get you to download something or add something to your browser that you do not want. Stick to the program in the center of the screen only.

2. You do not need to register or sign up for the site. It may prompt you to; ignore that prompt. Look for the free version on the page. You can get there by clicking My Account and then "Open," rather than signing in.

When you are done working in this program, you can save your work and download/export it to your device. The icons for these features are on the left side toolbar. Then you can share it back to your teacher through email or another method your teacher has requested.