Are these .pra file extensions related to Print Artist software?
Are these PRA files produced with a CAD software and you're trying to convert if to a PDF?
Are the PRA files that you're referring to being produced automatically by any MS Office software application?
Are the PRA files that you're talking about belong to the Microsoft Adobe Premiere 6.5 plug-in?
Normally and in any case you don't just open these type of files; you can , however, use Notepad or Notepad++ to examine its content. But the real answer should be to find that software that uses these type of file extension and install it in your computer.
.pra files are not (and should not be confused with) the usual executable files (.exe, .com, .docx, .xls, for example) that we, as computer users, are accustomed to work with on an everyday basis. Whatever the case may be , you're dealing with a specific piece of software.
Would you mind describing in more detail what are you trying to accomplish and what is the exact propblem that you're trying to work around?
If you notice in the discussion above Softech Inc. is mentioned as the producer of the software. If that would be the case you should be able to contact them through their home page: http://softech-inc.net/services.htm
The CADRA software doesn't seem to be sold as a software package by Softtech Inc. I may be wrong though. But it looks more like a custom made solution as part of the CAD modeling services they provide.
There is a CADRA software, however, that is sold by Mentor, a Siemes business partner or company.