Please compare a page from OpenMP 3.0 spec and a page from OpenMP 3.1. In 3.1 spec the font is severely horizontally compressed and spaces between letters are incorrect (some letters stick together -- and those are not ligatures, some letters have too much whitespace between them). That makes the text very hard to read.
The problem is, I think, that the 3.1 spec uses external fonts and my system doesn't have those available. Please, embed fonts in PDF: it is required to ensure that the document looks everywhere exactly the way it was typeset.