My GnomeSlackBuild don't recognize extensions
 

I have Slackware 12.2 with GnomeSlackBuild (I'm not happy at all)
When I try to open a PDF for example my gnome tries with gimp, when I open a png it open it with openoffice, I think my Gnome can't recognize extensions. It don't understand if I'm opening a jpg or a txt, when I download some wallpapers (jpg or png) gnome don't let me set the pics as wallpaper.
help me, i want to modify the extension database (if exists)

I newer had problems like this. Because I dont know where can you modify the whole database, but you can right click on a PDF file, then go to the properties, there to the Open With tab and there you can choose tath witch program you want to open PDF files. After this all PDF files open with that application. But you need to do it with other filetypes. To setup a picture go to the gnome-look.org and search for nautilus script to setup wallpapers