PHP MS-Word plugin

Hi everyone, I'm pretty sure that this question has been asked to death in the past, but I'm just curoius as to whether there is a plugin that can edit Microsoft Office Word documents in PHP. I'm interested in this because I am trying to put a text watermark on each page, but doing it online, without having to download the document, watermarking it, and then reuploading it (I won't deny that I'm lazy). So my question is has this even been done before? I've had a little search around and nothing exciting has popped out, so I'm wondering if anyone has used/heard of/made something as daunting as this before? Thanks in advance, DT