I hate the new 5.0, and am having the same issue. Because I created or opened and saved several documents in the new 5.0 before I realized how bad it is, I had to figure out how to make them usable again.
I have both versions of Pages (5.0 and 4.3) in my Dock for now. If a document tells me that it can't be opned by 4.3, I opn 5.0, open the document, EXPORT it in 4.3 with the same name, and overwrite the old document. That usually (big dog willing and the creek don't rise!) gives me access to my work.
Once I am sure I have no remaining 5.0 douments around, I'll take 5.0 out of the dock.
It truly is a pain in the ***. Here's the comment I left for Apple –
I am now attempting to uninstall Pages 5.0 so I can go back to using Pages 4.3. The designers of 5.0 took away (or hid) so many of the functions that I've come to know and trust that I am appalled.
It is now a kindergarten version of the workhorse I knew and loved. IT EVEN LOOKS like a dumbed-down app now, with cartoon buttons that reflect its audience – people who don't need a sophisticated, customizable publishing tool, who just need simple icons they can point at LIKE A FAST FOOD CASH REGISTER.
I'll be using either 4.3 or Word for Mac from here on out.