Files are not being recognized. Have read there might be a download of past PM apps available. Any confirmations?
Go to the Creative Cloud Desktop app, and select the Apps tab. Scroll down to Filters & Versions, then select Previous Version from the menu. Install InDesign CS6. It's the last version to open Pagemaker files.
Furthermore, consider this as your last wake up call!!!!
Pagemaker development and support was discontinued at least a decade ago.
At this point you should go through and convert any PageMaker content you think you will ever need to access since at some point, even InDesign 8 (CS6) won't run on future operating systems versions.