It depends on the year. From the 1970s into the early 1980s they tended to be Reynolds 531. That's only a general statement, though - there were exceptions. Afterwards, its probably either SL or SLX, depending upon the frame's size. For 1989-90, its probably a True Temper oversized tubing (I own a 1989 Paramount OS). After 1990, or so, they pretty much switched to Tange OS and a little Reynolds 753 OS briefly until the Waterford shop closed shop as a Paramount producer post Schwinn-bankruptcy. This all assumes its a Waterford-built Paramount. Since your's says "PDG" on it, it would probably be one of the later tubesets, and not a 1970s-era frame.
If you go to http://www.Waterfordbikes.com, they have a forum dedicated to Paramounts. Its the old Paramount factory under other ownership still dutifully producing some of the nicest steel frames around, and one of the Schwinn's is part owner. If you tell them the serial number, someone there on the Paramount forum should be able to date the frame and tell you what the steel was with a fair amount of certainty. They also have a provenance search feature where, for a fee, they'll search the old Schwinn records and try to tell you the frame's production history.
Take care,
Robert