How do I open a PageMaker document in InDesign CS5?

When I try to open a PageMaker document with InDesign CS5 (Mac OSX 10.7.5) I get an error message that it "Cannot Open file.... Adobe InDesign may not support the file format, a plug-in that supports the file format might be missing, or the file may be open in another application."  It's certainly not open in another application anywhere, It is, indeed, a PageMaker document which is supposed to be supported.  Before updating to current Mac OS, I used to be able to easily open this file with an old copy of PageMaker, but that no longer works on this OS!

Thank you!