∵BE = CF
∴BF = CE
∵四边形ABCD是平行四边形
∴AB = CD
∵AF = ED
∴△ABD≌△DEC
∴∠B = ∠C
∵AB//CD
∴∠B + ∠C =180°
∴∠B = ∠C = 90°
∴平行四边形ABCD是矩形