Some Paradox versions have universal backdoor passwords (also known as super / master / generic password), which come in handy in your situation:
# for PARADOX 7.0 use this password: jIGGAe or cupcdvum
# for PARADOX 5.0 use this password: same as for 7.0
# for PARADOX 4.x (DOS) use this password: nx66ppx
# for PARADOX 5.0 use this password: same as for 7.0
# for PARADOX 4.x (DOS) use this password: nx66ppx
You could also try a tool like this:
'Paradox Password Finder' (freeware, no source code)
http://www.rksolution.cz/Delphi/pxpassw.zip