I can guarantee from first-hand experience you that you will need to run the converter to open the files. I edited a small magazine a few years ago that was composed on PCs, but the firm that did our printing was all Macintosh. We had to run that converter every time we took files in to be printed. Macintosh files and Windows files are completely different and incompatible with each other. So once you open Pagemaker, you will need to go to Utilities/Plug-Ins/Publications Converter. Just follow the instructions.
One caveat -- this can take a long time. It's probably a lot faster now that processors and RAM have improved, but it took hours to do a 36-48 page magazine a few years ago. Also, the conversion process isn't perfect, or at least it didn't used to be. We always had to go back through the files and make a few manual adjustments to picture sizes, rule lines, type sizes, etc.
Hope this helps.