You may want to check out TeX and LaTeX which are open source standards for writing scientific and other types of manuals including Readers Digest. TeX gives you the flexibility of putting anything you want on a page without the difficulty of coding it in PostScript. Another nice feature is that it is a language that can be data driven so there are no point and clicks required to keep your manual up to date. We use it to generate PostScript and PDF reports with graphics etc... We have produced 5000-page reports, so volume it can handle.

I recommend A Gentle Introduction to TeX (PDF). If you read this document you will be able to get an idea if TeX is what you are looking for. If it is then look around in ctan.org for how to get started.