What I am understanding from your post is that you have some websites built wit plain HTML and you want to rebuild them with Wordpress so that you do not lose the SEO value of old pages/ content.
How many pages does those HTML sites have in total? If there are few (10, 20 or 30) then it is advisable to migrate the content manually by copy pasting. But if there are hundreds of pages then you should do this -
Create a new wordpress site where you want the content to be transferred.
Install the plugin named wp automatic.
Import all the html sites content in the new Wordpress site with the help of this plugin.
In the original HTML site, in .htaccess file add 301 redirect rules for the transferred pages so that the old urls will get redirected to their new destination and you will not lose any SEO value like age and keyword rankings of those pages.
You can search Google for how to edit .htaccess file to add 301 redirects.
If you find the above process too complicated then consider hiring some professional in the BHW forum.
All the best!
