public void RemoveUnusedFields()
{
Document doc = new Document();
//ExStart
//ExFor:MailMerge.CleanupOptions
//ExFor:MailMergeCleanupOptions
//ExId:MailMergeRemoveUnusedFields
//ExSummary:Shows how to automatically remove unmerged merge fields during mail merge.
doc.MailMerge.CleanupOptions = MailMergeCleanupOptions.RemoveUnusedFields;
//ExEnd
}