No version of PageMaker could ever edit PDF documents. As with other applications, PDF was only used as an output format.
Other than Acrobat, later versions of Adobe Illustrator can edit PDFs, as can some specialized prepress apps. Illustrator was once made for OS 9 so if you have that you could try opening them. However, it would open only one page at a time, and editing capabilities are limited.
It may be possible to use Acrobat Reader to copy and paste from the PDF into other applications, and some of them might read the data off the clipboard. For example, try pasting into PageMaker and see if you get anything useful. It works with some OS X apps.
Bottom line is that editing PDFs is not common because PDF was not really ever an interchange format, mostly a "no more edits, this is final" format.