How to add an extra field in outlook

I use Outlook for all my contact management.  There are many times when forms, made in MS Word, are created and are populated with the information from Outlook contacts.  Now I am wondering how to add a field so I can keep more information and put it directly to forms such as how much money someone has spent or something simple.  

I have tried to create a form and add fields however it only adds it to one customer.  How can I do it across the board?  

Thanks