(Reuters) - Chatham Asset Management said on Tuesday it had made a binding offer for RR Donnelley & Sons Co that would value the printing company at $663.4 million, outbidding a rival deal from investment firm Atlas Holdings. Chatham, the largest investor in RR Donnelley with a 14.9% stake, offered $9.10 per share for the remaining stock in the company. It had earlier presented a preliminary proposal of $9.00 to $9.50 a share. The move comes about two weeks after RR Donnelley agreed to be bought by Atlas for about $620.3 million in cash, or $8.52 per share. Chatham said it would raise its offer to $9.34 per share if the termination fee attached to the R.R. Donnelley-Atlas deal was waived off. Chatham also said it had filed a lawsuit against the companies to ensure an open and fair sale process. RR Donnelley and Atlas did not immediately respond to requests for comment. Chatham, which is also RR Donnelley’s largest bondholder, had earlier tried to engage with the company by asking it to replace directors and threatening a proxy war. Reporting by Chavi Mehta in Bengaluru; Editing by Aditya Soni