[Studebaker]

I have a document with a subject line that contains a patient's name
Ex: Subject: (First Name) (Last Name)

I've bookmarked the first name and the last name from the subject line
separately (I've called them FirstName and LastName respectively). I have REF
fields throughout the document where the patient's name will appear
(sometimes the patients first and last name will appear together and sometime
just the last name, i.e. Mr. (Last Name))

Can I put a certain kind of field or fields in the subject line so when I
enter the patient's name it will automatically bookmark the first name and
last separately so that the REF fields in the body of the document will pick
it up?
(I don't think I want to use the ASK or FILL-IN field with the pop-up box
b/c I don't know how to update it so it updates the doc automatically
everytime I open the doc to create a letter to a new patient.)