ChenPenghua

this app is simple but very strong, it gives your a "back door" to the WolframAlpha website ! All university students should have this app in their iPad if they mean to use thier iPad to study !!

it's easy to mark and even edit you pdf file. and it save your mark without enlarging the size of your pdf file. if you have noticed the size of pdf file edited by preview on Mac, you will strongly agree with me! i prefer to use Goodreader to mark and add pages in pdf file rather than using Mac preview. Also strongly suggest developing a Goodreader for Mac also.