Thanks Dinesh,
I did some research and found that the PXF file format is an export from Auto Pipe program. But the Bentley discussion posts of past describe some issues of data getting lost in round tripping data from Auto Pipe to Auto Plant based on the way the spec defines the components between the two software, see referenced post discussion in parenthesis. ("We can import files from Autoplant into Autopipe, but once we add modeling information such as P/T, load cases, SIFs, etc.... and send it back to Autoplant, we can't repeat the process without losing data that we have added to the file. In other words, the dimensional data remains intact, but we lose everything else except for support locations/types that have been added.")
It sounds like based on above that there is not much to gain by using the PXF file format unless I am using PXF files to transfer to and from Auto Pipe software only. So my understanding remains; If I want data from my client that I can work with in Auto Plant, to tie into and modify, I will need the Auto Plant dwg, spec and database files. And / or use the PXF file format with the Auto Pipe software.
Please inform if my above understanding is incorrect.