Let me see if I understand this logic you’re using:
The roswell incident was an alien craft crash, but it needed to be covered up, so a cover story was made to say the crash was from a legitimate government program from that era, which used materials that were described and photographed in available evidence at the time. A program which itself was ongoing and had unclassified elements, but had aspects of it which would remain classified for years after 1947.
And your evidence for this is a blurry rambling pdf file that a quick googling indicates comes from a British UFO “enthusiast” with no official provenance, and that has been considered bogus since the 1980s.
Extraordinary claims require extraordinary proof. If there was something not of this earth om that ranch at Roswell in 1947, the only way we’d know about it is if direct physical evidence shows up. Until then, the most likely explanation is the one that maps to the available evidence.