Okay, thanks to @blord-castillo and @artwork21 this is the final script that has worked for me!!
import arcpy, os, string, logging, datetime
from arcpy import env
path = "E:\\mappingtest\\raster\\" #Path to Raster
outPDFpath = "E:\\mappingtest\\out.pdf" #final PDF Output
env.workspace=path
mxd = arcpy.mapping.MapDocument("E:\\mappingtest\\mxddtet.mxd")
outputPDF = arcpy.mapping.PDFDocumentCreate(outPDFpath)
sourceLayer=arcpy.mapping.Layer("E:\\mappingtest\\raster\\update.lyr")
fcs = arcpy.ListRasters("*", "GRID")
x=0
for fc in fcs:
fc_lyr=path + fc[:-1] + str(x) +"_temp.lyr"
fc_pluspath=path + fc
fc_rl_temp=fc+"tp"
for df in arcpy.mapping.ListDataFrames(mxd):
for refLayer in arcpy.mapping.ListLayers(mxd, "*[insert-keyword]*", df):
arcpy.MakeRasterLayer_management(fc_pluspath, fc_rl_temp, "#", "", "#")
arcpy.SaveToLayerFile_management(fc_rl_temp, fc_lyr)
lyr_file = arcpy.mapping.Layer(fc_lyr)
arcpy.mapping.InsertLayer(df, refLayer, lyr_file, "BEFORE") # Insert New
arcpy.mapping.UpdateLayer(df, lyr_file, sourceLayer, "TRUE") # Update Symbology with example lyr-file
arcpy.mapping.RemoveLayer(df, refLayer) # Remove Old
PDFPath = path[:-4] + str(x) + "_temp.pdf"
arcpy.mapping.ExportToPDF(mxd, PDFPath)
outputPDF.appendPages(str(PDFPath))
x=x+1
outputPDF.saveAndClose()