The image you posted has clearly been tampered with. Notice the "03" in the date at top: Both the "0" and "3" are obviously in a different typeset (font) than the rest of the document. It becomes obvious when compared with the "3" in the zip-code at the top. There may be more discrepancies, but this one sticks out like a sore thumb.
Hannity just mentioned the possible fake letter along with FR where he first picked up on the story.