Hi Riccardo,

Riccardo Romoli <ric.romoli@gmail.com> writes:

> As in the wiky-emacs I added this to my .emacs:
>
> (setq TeX-PDF-mode t)
>
> but when I open a .tex nothing appens, pdfLaTeX is not enabled.

See the documentation:

,----[ C-h v TeX-PDF-mode RET ]
| TeX-PDF-mode is a variable defined in `tex.el'.
| Its value is nil
| 
|   Automatically becomes buffer-local when set in any fashion.
|   This variable is safe as a file local variable if its value
|   satisfies the predicate `TeX-booleanp'.
| 
| Documentation:
| Non-nil if Tex-Pdf mode is enabled.
| Use the command `TeX-PDF-mode' to change this variable.
| 
| You can customize this variable.
| 
| [back]
`----

The variable is buffer-local, that means you have to set in the relevant
buffer or you use

       (setq-default TeX-PDF-mode t)

to change the default value.

Michael