Andy_Langton - 9:14 pm on Feb 27, 2013 (gmt 0)
You would also be redirecting Googlebot if you do this, so your PDF would no longer rank.
If you opted to still serve Google the PSDs, it's definitely cloaking, and Google run automated tests to check for this (by pretending to be a browser with a Google search referrer). What you're proposing is to get Googlebot to rank content and then send visitors to somewhere you'd prefer them to be when they try to access the content that was ranked- the very essence of cloaking. I would proceed with extreme caution.
There's no tech issue, since file extensions are irrelevant. If you serve a .pdf as text/html it will open in a browser just like anything else.