Editing file in uni graphics [NX]

Help please, i have been downloading some files from the GRABCAD, but none of it i can edit using NX program ! Can someone please help me ! which file can be import to NX5 and edit ?!
Help please, i have been downloading some files from the GRABCAD, but none of it i can edit using NX program ! Can someone please help me ! which file can be import to NX5 and edit ?!