This is an eBook reader for Windows and Mac OS X. The application is absolutely free and it can open PDF files. It converts files and it changes their layout and formatting so that they are easier to read on your computer screen. It is a fact that computer screens are not designed for reading for a long time. That is why devices like the Kindle are so popular. GrassGames eBook Reader uses a darker background and softer fonts to minimize the strain to your eyes. It uses "font blurring" to make text smoother and help that way too.
From the menus, you can customize the background and fonts. I thought the default values were a big step forward in comparison with standard PDF readers. I didn't think my eyes were hurting when I tested the app.
One thing I did not like about GrassGames eBook Reader is that the interface wasn't really easy to follow. It doesn't let you use Finder to find your PDF files. You have to manually browse your file system to find them. The interface also felt a little slow at times.
All in all, this application works well, and it helps when reading PDF files on your computer. It is a free tool, so you can test it and see if it works for you.