Unless you already have Pages '09, you can get it from Amazon as the iWork '09 DVD for approximately $20USD. By itself, this is not compatible with Yosemite because the applications on the DVD are too old. So, once the DVD is installed, you download and run the Apple iWork '09 installer to get these iWork '09 applications to their latest revisions. It will give you Pages '09 v4.3.
The PDF manual for Pages '09 can be found here, not from the link on the Pages Help menu. Apple keeps rearranging the deck chairs. Because this is a discontinued product, Apple has changed many of the older links to videos, etc. to redirect to the Pages v5 page. Understand that Pages '09 has 100+ more features than Pages v5.5.3 on Yosemite.
Also, realize that the iWork '09 DVD applications are all discontinued products from Apple's perspective, and they are not taking pains to ensure that future releases of OS X will not break these applications.