You have 2 versions of Pages on your Mac and are alternately opening the wrong one.
Pages 5 is in your Applications folder.
Pages '09 is in your Applications/iWork folder.
Pages '09 can not open Pages 5, iOS 7 Pages, Pages for iCloud beta or iCloud files.
Pages 5 only runs on Mavericks and can not open Pages '08 or earlier files at all and alters/damages Pages '09 files, which once saved can not be opened by anything other than Pages 5.
Pages 5 files are in an odd compressed bundle, impossible to parse, which won't transfer via non-Apple servers. DropBox may have patched theirs, I haven't checked lately.
All Pages files, no matter what version or compatibility, have the same file extension: .pages.
Apple has removed over 90+ features from Pages and many of the rest are buggy. They have confused their users and apparently themselves with the installations, upgrades and cross-transfers of files. Effectively Pages 5 files are only compatible with themselves in a very narrow range of hardware and software.
http://www.freeforum101.com/iworktipsntrick/viewforum.php?f=22&mforum=iworktipsn trick
We are recommending users "upgrade" back to Pages '09 and trash/archive Pages 5 after Exporting their Pages 5 files back to Pages '09 or Word .docx files.
You should give Apple and other users feedback by rating/reviewing Pages 5 in the App Store.
In Australia approximately 70% of users say they hate it and it has hit 1.5 stars in the ratings and is sliding.
We are all waiting for an apology from Apple and some written direction of where it is going with this. So far nothing has eventuated.
Peter