Please note all iPhone/iPad users...you need to download the free app iBooks. Once you have downloaded that and you are viewing a PDF online that you would like to save, simply tap the screen. A grey bar will appear at the top of the screen. Select ‘open with’ in the upper right corner then choose iBooks. The PDF will then appear on your iBooks bookshelf. You can highlight and take notes using this app.
Android users...please download the PDF and it will be stored in the 'My Files' app on your devise.