Adobe Acrobat Reader Mobile App

If you have a tablet, you can use the Adobe Acrobat Reader mobile app to read for classes, as well as add annotations and notes to pdfs. To add annotations, follow these steps:

To access the Comments feature, click the blue icon in the bottom right of the screen:
Then select Comment from the drop-down menu:
You will see a menu at the top of the screen with various options, including a highlighter, the option to add text boxes, a pencil/pen to write on the pdfs, and a comment bubble to add comments:
Select the pencil icon from the menu at the top of the window and change the color/opacity as you would like:
You can also change the thickness of the lines if they are too thin or too thick by selecting the three lines to the far right of the menu:
Once you have adjusted the settings to your liking, you should be all set to write away!