There are two parts to an answer:
Word can read in html and export as pdf. The 'gold standard' for writing pdf files is Acrobat. It is likely we can import a lot of the text, but that we will then need to hand edit to improve it. For example, image maps will need work by hand for them to work in the pdf too.
Converting the entire manual is too much to do as a first step. We could instead convert a small part of it, first and offer that as a separate download. With experience from doing that we could ask for volunteers to help us do the whole manual - and possibly translations too.
A significant issue is that the manual is constantly being revised. Therefore we want to automate as much as possible of the conversion, because otherwise there is a lot of work with each new version of Audacity and the manual.