That's exactly why they want it as a Word document. That's what they use to produce their in-house resumes for distribution, and they don't want to waste ten seconds on opening an HTML or PDF resume in Word and selecting "Save As... Word document". They want to create their own resume, with your name on it, that is loosely based on your actual resume, so they can send it out to hiring managers.

It's very safe to say that if you don't know how to open and edit a PDF document, you have no business being a tech recruiter. Anyone foolish enough to be represented by such a person while looking for software jobs is going to have a bad time.