Thanks for your reply.
For fix it, first i've added the line 'PDF' => 'application/pdf' to the static property $SUPPORTED_FILETYPES.
But, the pdf file format could be upload only with the gdata Version 3.0.
That's why I asked for an official solution, and not a patch made by myself :D
I've found a rebuild of the Zend_GData_Docs on the net, which implements the protocol version to use when calling google document api.
That's why I was surprise that the last version of GData didn't implement it.