Call notesdoc.ReplaceItemValue(“FullName”, FirstName + " " + Surname) should work, IF FirstName and Surname are variables you’ve defined and set somewhere else. Otherwise, you’ll need
The only real reason to go the long route with ReplaceItemValue is if you have more than one NotesItem on your document with the same name. In that case, ReplaceItemValue removes all of them and creates a single new item with the new value you assign.