You should probably first contact the company that supplied your PxPlus. Generally PxPlus (or its predecessor ProvideX) came as part of a business application. Your application supplier should be able to advise you on the latest version of PxPlus they are using and how to obtain it.
Version 6.30 is a very old release and no longer supported however you may be able to find a copy of it at https://archives.pvxplus.com/
As for accessing the data there is an ODBC driver available that should allow you to access the files along with a command line processor PXPSQL that allows you to execute SQL commands against the file structure and get the data out.
One thing should be noted though, the ODBC driver and PXPSQL utilities rely on the system having and using a Data Dictionary (Schema definition) . Some older applications neither use nor come with the data dictionary so this may not be a option for you. In this case your original application provider may have to assist you or you may be able to find others on this forum that can.