Hi,
I would like to know how to insert only part of the file name into my work document. I know how to and use the function Quickparts/filename...this gets me part of the way. My file name is for example is "Q123 - New document"
I would like to only see Q123, or anything before the first space and not the " - New document"

You cannot do this with only a field. You could potentially have an AutoOpen macro that inserts the part you want into a document variable and use a DocVariable field to display it in your document. You would want that macro to update the field whenever the document opens.