In one of my stories, I have a letter written by a girl's adoptive father. She loves him, he is pushing 80, but he tells her he is dying, along with other information he thinks she should know about her past and parents that was never before revealed to her.
I presented the letter in italics (used to indicate thoughts) as she read it, I add 1 inch to the left and right margins for any letter content. I broke in-between (with normal margins) to break that up with some exposition, her reactions and other thoughts as she read (e.g. she stopped reading to cry at one point), and when I came back to the letter went back to the wide-margin italics, with an ellipsis ... and repeating the last line she had read.
My rationale is that when she is reading, the words she is reading are going through her head as thoughts, so they can be presented as such, and the extra margins make it easy for my audience to tell "letter" from "exposition" and "other thoughts" of the character.
Also, the exact format of the letter doesn't matter to the story, what matters is the information imparted to the character. He asks her to do something, and she does love him and can't turn him down, but it will be complicated...
The important thing is to be clear, and for the purpose of submission you should NOT go to other fonts or picture inserts, etc. To me this was the least intrusive way of clearly setting the letter apart from the normal text and dialogue of the book.