how do I save an old document in Pages 09 first?

Are you currently using Pages 09 or Pages 5.X?

Or are you looking to save a document in Pages 5.X in 09 format?

If you are dealing with a Pages '08 document and find that Pages v5 no longer supports it, here are your options for reading that content in Pages v5. Pick the best one for you:

• On a machine with Pages '08, export as an MS Word (.doc) document
• On a machine with Pages '09
  • Open and save as a Pages '09 document
  • Open and export as an MS Word (.doc) document
• Upload the Pages '08 document to the free zamzar conversion service, and receive a downloadable .docx via email link in about 4 minutes.
• Install the iWork '08 DVD on your current machine (including Yosemite) then immediately update with the following:
  • Pages '08 v3.0.3
  • Numbers '08 v1.0.3
  • Keynote '08 v4.0.4
• Purchase and/or install the iWork '09 DVD
  • Immediately apply the Apple iWork 9.3 updater.
  • Some Pages functionality lost in Yosemite.

New installations of iWork '08/'09 DVD, and updates should be followed by Disk Utility to verify/repair permissions.