In the episode, "I Remember You", as you know, Marceline finds a newspaper article about Simon Petrikov. I have decoded (most of) that article.

Here's the original picture:

I Remember You Newspaper Clipping

And here's what it says (~~ is where it's illegible):

Simon Petrikov Unearths Ancient Treasure

Silly man returns from expidition with a marginally exciting discovery.
By Bruce G~~

It was~~or~~g that gree~~th~~of hard-dr~~halists~~curious pigeons.
T~~orr~~otu press conference was conven~~professor of archaeology~~nd bon viva~~ Simon Petrikov.
You may remember Petrikov from ~~t thing F~~nva.
Well that g~~ from his ~~to~~ expedition in the ~~dd~~ or wherever.

With much pomp~~ Petrikov unveiled the most significant ~~ce from the dig to a rapt ~~dd~~nce~~ ou~~ it was just a book.
A ratt~~fou~~ng~~ leatherbound manual whose title ~~eriff~~ had trarr~~a~~d as "Tne Enchiridion".

The cove~~wid~~a still life ~~d ins~~ w~~ va~~ c~~y of gerris was alrip~~ loo~~

"The book seems to contain rules of conduct~~

Simon Petrikov delivers his latest find to the ~~ Museum of History