External PDF viewer (Mac OS)
As most of the Mac users I used Preview to open and read PDF files. However, when working with scientific articles I prefer using Skim as it's marking and annotation capabilities are much greater than those offered in Preview. It would be nice if I could configure Zotero to open PDFs in Skim instead of Preview. I know I could achieve that by making Skim default PDF viewer but I want Preview to be default application for reading PDF files, it's integration with Safari and Firefox PDF plugin is really handy. Not to mention that it's simply very neat and handy application. Skim is good in working with big files like books or long articles where all the annotation and marking features come in very handy.
http://www.zotero.org/support/hidden_prefs#general_preferences
otherwise you''re pretty much out of luck - best choice then is to use "show file" and "open with.."
Perhaps you can find some sort of conditional opening tool, though I don't think I've ever seen such a thing.
It still seems that, assuming one uses ZotFile, in order to open the pdf at links (e.g. imported chapter headings), one will need to adjust the ZotFile advanced settings.
Does Zotero provide this function of opening the pdf at links without ZotFile?