Transfer old site data into new wordpress site

Hi, I’m not sure if this is the right forum section, but I’ll try anyway.

My client has a very old site (age around 1999) that uses table and frames. The content is managed with .htm. Every links opens .htm page, so it is a huge mess!!

Have you any suggestion for take all data and import (not one-by-one) in a new site build in WordPress? What is the best way to do this?

Thanks