Try this. It is not 100% but it works for me in most situations. I have PageMaker 7.0 in Windows Vista (similar to Windows 7). I'm still looking for a better solution but in the mean time, at least I can export most PageMaker 7.0 (.pmd) documents to Adobe PDF.
Go to Control Panel - Printers
Right Click in an empty spot - select "Add Printer ..."
Choose "Add a local printer"
Check box "Use an existing port"
Select "FILE (Print to file)" (you can experiment but I used this option)
Click Next
Under '"Manufacturer" - Choose "Generic"
Under "Printers" - Choose "MS Publisher Color Printer"
Click Next and finish out the Wizard
Good Luck