Bankrupt National Envelope agreed yesterday to sell its operating assets, including a plant in Fayette County, Pa., to competitor Cenveo Inc., the world's largest envelope manufacturer, for $25 million, The Tribune Review reported yesterday. Both companies have been affected by the rise of email and online bill paying, reducing the demand for paper envelopes. National Envelope, based in Frisco, Texas, said that it reached a definitive agreement with Stamford, Conn.-based Cenveo to sell most of its assets for $20 million in cash and $5 million in stock, which is expected to occur by the end of September, subject to bankruptcy court approval. The company's parent, NE Opco Inc., sought chapter 11 protection on June 10 for the second time in three years. Cenveo said that it expects that the acquisition of National Envelope will increase sales by about $300 million and operating profits by about $30 million once the two companies have been combined.