When dtSearch indexes a document that contains fields, all fields are automatically made searchable. 

Additionally, you can use StoredFields to designate certain fields as document properties that should be returned in search results. 

For example, if you make "Subject" a stored field, then the SearchResultsItem for each email message indexed will include the message Subject in SearchResultsItem.UserFields. StoredFields expressions can include the wildcards * and ?. The maximum amount of data to store for a field is controlled by Options.MaxStoredFieldSize.

IIndexJob Interface