Worcester Envelope Co. has sold part of its Auburn headquarters property to its new owners for just over $5 million in a deal closed the same day the 125-year-old company announced it was sold. Worcester Envelope, which makes direct-mail envelopes, was bought by Moore DM Group, a marketing firm with locations across the country, in a deal announced in mid-February. The sale of roughly half the company's Auburn headquarters, which is split in two buildings on two adjoining parcels, closed on Feb. 12, the same day of that announcement. The owner is a limited liability corporation registered to Moore's Oklahoma headquarters. The company couldn't be reached for comment.