Pages '09 v4.01 thru v4.3 is a 32-bit application, and is not supported on macOS Catalina 10.15.0 - 10.15.7 as the operating system only supports 64-bit applications. Documents created by Pages (any version) are data and neither 32-bit, or 64-bit.
Once you have opened a Pages '08/'09 document in Pages versions from v5 thru v10.2, and attempted to change anything, then granted the application permission to convert the document format, the original Pages '08/'09 document format ceased to exist — unless you have a backup copy. These new documents are not directly backwards compatible with Pages '08/'09 applications.
You have not expanded on what destroyed implies, and whether there remains help available to resolve it.
If you had performed a Time Machine backup of your previous operating system (e.g. Mojave) to an external drive, before upgrading to Catalina, then you would have a practical means to revert your Mac to a previous macOS version. Without that Time Machine backup, or a standalone backup of your Pages '08/'09 documents, you will have to wipe your Catalina drive, and reinstall the previous operating system, with potential for current data loss.
