Funnily enough on my FreeBSD desktop there is a libpagemaker installed as dependency for LibreOffice and Scribus (an open source DTP program). I remember it being installed and it raised a curious eyebrow for me. So it seems that both of those programs would be worth trying. YMMV. I'm guessing they would be able to extract text as a minimum.
Aldus Pagemaker 5.0 Swe 64 Bit