To rescue some information from a corrupted document, you can right click (ctrl-click) on the corrupted document and choose "Show package content" and look for a file called index.xml or index-new.xml. Copy the xml file to the desktop (for example) and open it with TextEdit. The content does not look nice, but text you have entered is partly readable.
If you only have a file called index-new.xml you can try the following steps:
- Copy the entire corrupted document, so you have a backup just in case.
- Rename the file index-new.xml to index.xml (with or without gz depending on the original).
- Open the file in Pages.