This is not written to be run in Script Editor.
There are two parts of that script that need to be pasted (in order) with an intervening blank line into Script Editor. As this script is designed as a drop folder application, it is saved as an application to your Desktop, where you drag and drop file(s) and/or folders containing Pages documents onto it. The resulting PDFs are written in the original Pages document locations. Any damaged Pages document very likely will abort the application.
I just copy/pasted both parts of this script into Apple's Script Editor. Initially, I saved it as an .applescript text file so I had the editable source available. Then I used option key + Save As to save it as an application on my Desktop. I dragged a couple of Pages documents from a folder onto the application and it converted them to PDF correctly with the final dialog reflecting that status:
Tested on macOS Ventura 13.2.1 with only one change to the original script. In part 1, I changed display alert to display dialog. That is all. Other than the typical security dialogs about allowing the script or pages access to the documents, there were no error or warning dialogs.