I want the form to generate a new number for the people i send it to when they open the form i want it to have a  number in the client id field.  i want the number to not change if they email it back, print it or save it. just has to be different for each person

I am using adobe acrobat 8.3 i want to make a new form that will auto add a unique number to one field when the file is opened. the name of the field is "Client ID"  i have searched and searched and searched and yet i am at a loss i need some ones help, i am not understanding any thing i am reading...