Opening PDF's in NS2

vining

When opening a PDF file in NS2 it always launches Adobe Photo Shop and not the The Adobe Reader which is currently Adobe Reader 8.1 on my PC. If I go to Windows Explorer>Tools>Folder Option and scroll down to the .pdf extension it show Reader 8.1 as the application for opening this file but despite this every time I try to open a pdf file in NS2 I'll still get PhotoShop. Is there a setting somewhere in NS2 I can change? It's making all the reference files I keep in the "Other" area of the workspace pretty much useless. It does open .doc's correctly but most of my references are manufacturer's pdf's.