Here are two translations of the same section of the letter to Menoeceus. The left is the Epicurus wiki at Epicurism.info and the right is Cyril Bailey's "Epicurus the Extant Remains." I am not able to offer an opinion in the Greek original, but I can offer an opinion on the English wording:
The English wording presented here equates "pleasure" with "absence of pain" as if the two concepts were interchangeable in every respect. My contention is (1) that it is clear to any "normal human" that the two concepts are clearly NOT interchangeable in every respect, (2) that Epicurus was in every relevant respect a "normal human," and (3) that therefore there is (a) some corruption of the text, (b) some corruption or inadequacy of the translation, (c) some missing context that explains the apparent discrepancy, or some combination of (a), (b), and (c).
Note also that this text, even in its current form which appears to equate the two terms, does not state that "absence of pain" is "the highest pleasure" as seems to be regularly assumed in writing on Epicurus. In neither translation is it stated that "the goal" or "the end" is "absence of pain" unless one adds a third equivalency ("pleasure" = "absence of pain" = "the goal / the end") which is also counter-intuitive.
I believe the relationship lies not in "equivalency" but in "quantity" as is referenced in PD3, but there is no doubt that the current English translations are written as if the meaning were clearly "pleasure is equivalent to absence of pain."
If you have the knowledge of Greek sentence structure to comment on how the wording does or does not suggest equivalency, please post your comment. And if you have another theory on how to reconcile this please post that as well.