Final pe (ף) always has an F sound. For a P sound you have to use the normal פ, even at the end of a word. This only happens in words and names of foreign origin that were transliterated to Hebrew, as normal Hebrew words will never end with a P sound.
Are there any words that end in a P sound that aren't borrowed from other languages? If so, is using the פ at the end of a word only applicable when not using a dagesh?