解:过点$C$作$CM\perp P D$于点$M,$过点$E$作$EN\perp DF $
于点$N,$则$∠CMD=∠DNE = 90°,$
点$E$到$DF $的距离为$EN$的长
∵$∠CDM+∠DCM = 90°,$$CD\perp DE$
∴$∠CDE = 90°$
则$∠CDM+∠EDN = 180°-∠CDE = 90°$
∴$∠DCM=∠EDN$
又∵$CD = DE,$∴$\triangle CDM≌\triangle DEN(\mathrm {AAS})$
∴$DM = EN$
∵$CM\perp P D,$$CP = CD,$$P D = 8$
∴$DM=\frac 12\ \mathrm {P} D = 4$
∴$EN = 4,$即点$E$到$DF $的距离为$4$