Stuff has been forged on both sides of the fence. What usually sinks it, is the contents, because it is the answer to the wish.
'I sure wish I had one that said >insert x<.'
Poof
'Oh look, I have found it all here in this one document'
Sometimes the document even has the correct seals, signatures etc. What it doesn't have? Patents and confirmability...
viewtopic.php?t=207
It happens man.
I also don't have to give a forgery artist any props. It is tradecraft. I would fully expect a professional to use correct paper, ink, equipment etc.