Automatically update field codes

[Lgoo]

Hi,

I work for a company that has many form business letters that we use
every day.
While the date field usually automatically updates, I would like there
to be a way to automatically update the username of the person and
posibly the title of the person using the document.

Example end of document:

---->

Sincerely,

UserName
Title

While I see that there is a field code for username, is there a way to
write a macro or something that auto updates this field on open without
having to select it and press F9? I've tried the AutoOpen macro with:

ActiveDocument.PrintPreview
ActiveDocument.ClosePrintPreview

but this does not seem to work.

Any thoughts would be greatly appreciated.

Thanks,
Larry