[TYPO3-english] referring fileadmin pdf files

[Francesc Juliana]

Hello everybody:
I have several pdf files uploaded in fileadmin folder.
When I want to use them as files in sections or in extensions an error 
appears. It says :
File extension 'pdf' not allowed
If I upload an external pdf file in section or in extensions the error 
doesn't appears and the file is being attached to section.
This happens only when I refer an internal fileadmin pdf.
In $GLOBALS['TYPO3_CONF_VARS']['GFX']['imagefile_ext'] variable I have pdf 
included in his value.
I have cleared all cache.

Anyones knows why this happens?

Thanks in advance.

Francesc