Expand AD to m so that DM=AD,

Because of the edge, BD=CD, ∠ADC=∠MDB, AD=MD,

Therefore, the triangular ADC is completely equal to the triangular MDB.

So ∠CAD=∠BMD BM=AC

Because AE=AF

So ∠CAD=∠AFE

Because ∠BFD=∠AFE

So ∠CAD=∠BFD

So ∠BMD=∠BFD

So BF=BM

Because BM=AC

So AC=BF