(1)解:∵△ACE≌△DBF,∴AC=DB,∴AC-BC=BD-BC,即AB=CD,∵AD=10,BC=4,∴AB=(10-4)÷2=3,∴AC=4+3=7;(2)证明:∵△ACE≌△DBF,∴∠A=∠D,∴AE∥DF.