Pages '09 cannot open any document created, or converted by Pages v5, or v6, because the document architecture does not contain an index.xml internal file, and the documents are not backwards compatible.
If you have Pages v5 installed on your Mac, then actually quit Pages '09, and then double-click this document to have it opened in Pages v5. Then export to Pages '09 format. An alternative is to right-click on the document, and then follow the Open With submenu to the correct version of Pages.
If you do not have Pages v5 installed, hop out to iCloud dot com, sign-in with your Apple ID, and open this document with Pages for iCloud, and then download as a Word document that you can open in Pages '09.