Planetary Historian Trophy in Lifeless Planet

There will be more than 20 documents that you can collect while going through the game. Most of these documents will be right in your path. They look like either tape recordings or pieces of paper. There will be a bright white shining light coming from it as well to indicate where it is located.

If you haven't obtained this trophy by the time you've gotten every other trophy, you can use chapter select and pick up the collectibles that way.