The software company Adobe Systems said on Monday it was doubling the maternity leave it grants, making it the third company in the American technology industry in a week to give new parents more paid time off. New mothers at the California-based company will receive 26 weeks of paid leave, up from 12 weeks, and primary caregivers and new parents will get 16 weeks of paid parental leave. “We join an industry movement to better support our employees while striving towards increased work force diversity,” said Donna Morris, an Adobe senior vice president. Adobe has 13,500 employees globally, including 6,500 in the United States. About 30 percent are women.