Returns or sets the text that's displayed in a message box when the form field has the focus and the user presses F1. If the OwnHelp property is set to True, HelpText specifies the text string value. If OwnHelp is set to False, HelpText specifies the name of an AutoText entry that contains help text for the form field. Read/write String.
Example
This example sets the help text for the form field named "Name."
With ActiveDocument.FormFields("Name")
.OwnHelp = True
.HelpText = "Type your full legal name."
End With