Microsoft's Office for Mac is a paid subscription (Office365), or single purchases of Office 2016 for Mac, or Office 2019 for Mac. Only Office365 subscription versions of the Microsoft applications are available from the Mac App Store. All of these Microsoft applications are supported on macOS Sierra (10.12) or later.
LibreOffice is a free MS Office Suite clone. It will install on your Yosemite installation. This is the best Word document compatibility solution when you don't have Microsoft Word at home.
If you don't have Pages, then you can't get it from the Mac App Store because that current requirement is that you have macOS High Sierra 10.13 or later installed. Apple does not retain past, full Pages installers.
You could purchase from Amazon or Ebay resellers, the retail Apple iWork '09 DVD, and then subsequently update that installation with the Apple iWork 9.3 updater. Personally, I would recommend the free LibreOffice solution, and take advantage of the well written PDF user guide for LibreOffice Writer 6.0.