A: Yes, but it is difficult. Grammar books require "fixed layout." A scanned PDF will look tiny on a 6-inch Kindle. Use a tablet (iPad/Android) or a computer for PDFs.
A: The 5th edition (2019) has updated text, new illustrations, and a more modern layout. It also includes "Interactive eBook" access. The 4th edition is still excellent, but the 5th is superior.
If you are a visual learner who likes to scribble notes in the margin, buy the physical book. If you are a commuter who studies on the subway, buy the official digital version. How to Use the Book for Maximum Results (PDF or Print) Downloading the PDF is useless if you don't know how to study with it. Most people fail because they read it like a novel.