Poltahr's Notes is a tome found in Act II of Diablo III, inside Poltahr's Satchel in the Chamber of the Lost Idol. The Satchel may be in any part of the Chamber, not necessarily near the exit or the Idol.
This tome is required for the Judge of Character achievement.
It reads as follows:
I never thought I'd become a treasure hunter, but I also never thought my family's fortunes would sink so low. Yesterday I heard a nobleman asking about The Rygnar Idol — an artifact that belonged to the great mage Zoltun Kulle. If I can retrieve it, my family will never go hungry again. — Poltahr