Fields.Add (Word)

Adds a Field object to the Fields collection. Returns the Field object at the specified range.

You cannot insert some fields (such as wdFieldOCX and wdFieldFormCheckBox) by using the Add method of the Fields collection. Instead, you must use specific methods such as the AddOLEControl method and the Add method for the FormFields collection.

Syntax : expression.Add (Range, Type, Text, PreserveFormatting)

Selection.Collapse Direction:=wdCollapseStart 
Set myField = ActiveDocument.Fields.Add(Range:=Selection.Range, _ 
 Type:=wdFieldUserName)

Arguments

The following argument is required

Range (Range) - The range where you want to add the field. If the range isn't collapsed, the field replaces the range.

The following arguments are optional

Type (WdFieldType) - Can be any WdFieldType constant. For a list of valid constants, consult the Object Browser. The default value is wdFieldEmpty.

Here you can find possible values for WdFieldType.

Text (String) - Additional text needed for the field. For example, if you want to specify a switch for the field, you would add it here.

PreserveFormatting (Boolean) - True to have the formatting that's applied to the field preserved during updates.