I got all of this from Neogaf. :D
Here's the official game package sent to the press for reviews:
Transcription of letter:
Dear Friend,
I'm glad you've taken the time to open this book - it's more interesting than it looks from the cover, right?
However, the fact that you've found it means that I'm in trouble and I desperately need your help. I'm Nathan Drake, a treasure hunter by trade. I'm writing this letter as insurance tonight - tomorrow, I set off on what could be the biggest expedition of my life.
I can't tell you exactly where I am as I am following the trail of my ancestor Sir Francis Drake, who's been dead for four centuries. My mission and my fear - is to find his last treasure. And where there is money there is always trouble. All I know is that it's an island in the Pacific - an island that could contain the greatest treasure the world has ever seen.
Please keep this diary safe - it contains everything I have collected thus far regarding Sir Francis Drake's disappearance. A lot of people want to get their hands on this information, so you would be wise to not contact anyone regarding the diary. It's not safe to go to anyone in my business.
God willing, I will thank you in person - and, of course, reward you for your help.
Nathan Drake