Battered by competition from Internet retailers and burdened with too much debt, Borders Group Inc. filed for Chapter 11 protection Wednesday with plans to close about 30% of its stores and emerge with a new focus on e-books and non-book products.

The operator of Borders and Waldenbooks stores blamed lower consumer spending and fierce competition. Whether it can emerge as a stand-alone company will depend in large part on its ability to operate its stores more efficiently while growing Borders.com and making itself a destination...