file.lgx
The LGX extension was used by PCAD for a while. It stood for laser-Gerber-RS274X.
As I recall, Orcad comes with Gerbtool Gerber Editor. You can use that to open the Gerber files.
If you have trouble with Gerbtool, you can also use my favorite which is free to download. Pentalogix Viewmate has a much cleaner and easier interface than GC-Preview or Gerbtool - it also does a better job of reading some of the more obscure G-Codes that can sometimes be found in Gerber files. You can download it free at: **broken link removed**