.dxf open issue (see the details below)

[Petrik_Kollar]

I found the solution in other post

Installation & assoc problem

Do you have Rhino 4 installed? Rhino V4 and V5/32 unfortunately have the same executable name - Rhino4.exe - so the system can get confused. The dxf/dwg association was also an issue at the beginning of Rhino 5 with early versions, so if oyu installed form the CD, make sure you have both 32 and 64 bit versions of V5 updated to the latest (SR12). –Mitch