Hi Lou, That seems to be a personally prepared, signed, and notarized statement/affidavit by Arthur Todd attesting to the fact that he, and only he, personally witnessed Mosconi's run. The seal is likely the notary seal.
Jimmy, while I think you could read it that way, paying particular attention to the typed portion of the affidavit, I believe the side of the document with the signatures speaks for itself were it says, "This is to certify that on this date the undersigned witnessed Willie Mosconi make a run of 526 on a 4 x 8 Brunswick pocket billiard table in the East High Billiard Club in Springfield, Ohio."
Lou Figueroa