There were lots of extra Book of Secrets documents, from different presidents, and referring to different events, real or not. This is some of the stuff that refers to Area 51. The alien autopsy ‘photo’ was created by my intern Bryan Morton. We also created lots of ‘fake moon landing’ photos and documents.
No reference was made to that in the script, we just did it for fun, but the director liked it and incorporated it into some scenes. Alas, like most of this stuff, it didn’t make the final cut.