Basically you are going to create a FM script that runs an AppleScript that opens your numbers or pages document. Then you are going to link that FM script to the button.
The AppleScript will look something like this:
tell application "Finder"
open document file "filename.pages" of folder "Financial" of folder "Documents" of folder "matt" of folder "Users" of startup disk
Alternatively, you can insert the file into a container field on the contact record as a reference only. That way, when you double click the container field, it will open the document in its application (numbers or pages).