PDF file and Netscape

I have a friend who downloaded a doc that needed Adobe Acrobat Reader. He downloaded that software, went to open the doc. and recieved a message saying he needed Netscape to read. He uses Explorer. Other than downloading Netscape, is there another way to work around this? It sounds to me like it might be a security thing and that it might have been saved as a PDF only to be opened with Netscape. Does anybody have any insight?
Would appreciate knowing why?

Tia

Melonie