Well, my thought was, even if it is 50-100 pages, if the content is relatively straightforward (i.e. no embedded charts and graphs) they can control the word doc and then just send to you when it gets updated. You place the MS Word doc with it’s defined styles into your template and for the most part the hard work is done.
I feel your pain though. If you are an in house designer this sort of thing comes up a lot. They want the look of a well executed and branded design, but they want to do what they always do which is mess with things in Word (or PowerPoint).
I actually recently created a PDF form for a one page bio of sorts for some of our employees and it works well, but that is because it is a single page and not a multi-page piece. IMO PDF forms work best for simple one (or maybe two) page documents or (surprise, surprise) for actual forms (such as the sort of form you might fill out at a doctor’s office for example.)