Q: How do I convert an English document into French?

One method would be to use Google Translate. There is a "translate a document" link right below the left text box at: https://translate.google.com

I couldn't get it to work directly on a Pages document or on a Pages document exported to Word format (although it does work on a document actually created via Word). It did work on a Pages document exported to either PDF or TXT format however.

Note that machine translation, such as Google, is good for getting the general idea of an document. If the document is properly spelled, punctuated, grammatically correct and doesn't use much slang, you should be in pretty good shape. However, it's still not a replacement (yet) for proper translation by a person.