There is no logic at all in converting to word and then converting to PDF
All you would be doing is increasing the risk of creating formatting errors
If you are happy with the layout, print directly to PDF files from within WordPerfect using one of the PDF converter programs. That will minimise the risk of introducing new errors
Remember - Word 6 is an ancient DOS program, the file format is unsupported now. You shouldn't be thinking of using that
And on a total aside, if you intend to publish further books, learn to use LaTex, or its Windows version MiKTeX
About MiKTeX - MiKTeX Project Page Using that means you don't have to worry about fonts / styles / layout. Thats all dealt with by the typesetter - all you as the author then have to worry about is the actual text itself
Too late to use it now, but remember for next time. Many (most?) scientific journals or articles are created using it, as it enables a "house style" to be easily superimposed