dear Reyalino,
put
df = arcpy.mapping.ListDataFrames(mxd)[0]
before "for loop",
import arcpy
arcpy.env.workspace = "D:/Directory/Map"
mxd = arcpy.mapping.MapDocument("D:/Directory/Map/layout.mxd")
listFC = arcpy.ListFeatureClasses()
df = arcpy.mapping.ListDataFrames(mxd)[0]
for fc in listFC:
layer = arcpy.mapping.Layer(fc)
arcpy.mapping.AddLayer(df,layer,"TOP")