nPDF not working properly

Hi there.
I can't seems to get nPDF to work. I have Ndless 3.6 installed on my Nspire CX. I downloaded and transfered the nPDF files to my calculator, clicked on the icon i my documents, and it said that the file Extensions were now installed on it. But when I try to transfer a .pdf file to the calc I get an error Message saying it is not supported.
Any help?
I can't seems to get nPDF to work. I have Ndless 3.6 installed on my Nspire CX. I downloaded and transfered the nPDF files to my calculator, clicked on the icon i my documents, and it said that the file Extensions were now installed on it. But when I try to transfer a .pdf file to the calc I get an error Message saying it is not supported.
Any help?