The file is associated with OPIM program, and as mentioned before if you open the file directly from a shortcut, from Windows Explorer, from inside OPIM, etc.. then you will incur an OPIM usage charge.
In the past, there was an extra AutoPIPE Stress Iso Add-on license required to create a Stress Isometric within AutoPIPE. This has since been incorporated into the program cost for Advance and Nuclear editions. OPIM is a completely separate product from Bentley that requires an entirely different license. In order to keep things separate, AutoPIPE can export and view a Stress Isometric in OPIM, however the commands must be initiated from within AutoPIPE to avoid an OPIM usage charge.
The only official method of creating and opening an Stress Isometric demonstrated HERE.