Here's some reference pics for anyone who decides to take on this project. Eve's letter can be seen at the beginning of Season 1 Episode 1 and the other letters can be seen at the end of Season 1 Episode 2. The border on the letter looks magenta or purple but the Metropolitan Public Library header is black. The envelope has a gold foil lining and the library's logo in the upper left corner. Eve's letter is the only one with a stamp and her name (written as Col. Eve Baird) on the outside. The full text of the letter says:
You have been selected
to interview for a
prestigious position with the
Metropolitan Public Library
It would be cool to do a version with gold foil lettering to make the text "glow."