System Five Pervasive database files have the file extension .btr
Not all .btr file are Pervasive database files however.
Database files over 2 Gigabytes are split into multiple files with the hexadecimal file extensions
btr ^01 ^02 ^03 ^04 ^05 .. ^09 ^0A ^0B .. ^0F ^10 ^11 .. ^FF
When rebuilding large files, use the file rebuild utility that is in System Five. Do not use the bcopy32 program as it is not aware of extended files.