[AUCTeX] Auctex treats tex file as plain tex files

[Damian]

Hello,

I don't know why, but when I load a tex file, I see the syntax
highlighted and the mode in emacs reads PDFTex. But auctex seems to be
inactive. The keyboards shortcuts don't work when editing those files,
but they work well in the others.

I have no idea what the problem may be.

Thanks in advance,
Damian.