Pages Quit Unexpectedly- using Yosemite 10.10.5
Create a new user account, and run Pages from there.

If that works, then the problem is localized to your user account.

If that is the case, quit Pages and try deleting the cache file at

~/Library/Caches/com.apple.iWork.Pages

where ~ stands for your user account. Use the Finder’s “Go To Folder” command to get to ~/Library/Caches and then look for the appropriate folder.

If that doesn't work you may have corrupted preferences, which can be found at 

~/Library/Preferences/com.apple.iWork.Pages.plist

which you can also delete (or move to your Desktop while Pages is not running).

(These suggestions assume that you are running Pages from the Mac App Store, not the iWork '09 version.)