Is there any recommendation about the direction of swipe for an app that allow user to read PDF documents? I mean if I have to chose is better the up/down or the left/right swipe?
In my own experience I prefer apps that allow me to swipe up and down to go through the document's pages. This is because sometime is more comfortable to scroll the document e watch the last part of the previous page while i'm reading the current page, this happens usually when the previous sentence / paragraph is cross pages. On the other side well crafted app like iBook allow only the horizontal swipe gesture.
It will be great if you will able to cite some research about this topic
Edit: On 23 October 2012 Apple introduce iBooks 3 which brings as new feature the continuos vertical scroll. I think this is relevant to the scope of this question.