I've had the same problem with getting rid of a watermark for a set of PDF's I had, but since, more times than not, the PDF you will have is an image version, there is no quick 'n easy way to get rid of them. Your problem sounds like it's still in non-image form, if only the watermark is showing up, so you might be able to get rid of the watermark using techniques you find off Goodle; e.g., Adobe Pro -> Tools -> Remove Watermark, et al, but if it isn't, then it's time for some fun! If the watermark is a different color than the rest of the text (as in my case), you can simply open the PDF in Photoshop and get rid of the channel the offending party resides in. If it's the same color as the rest, then it's more tricky. In that case you will probably need to run OCR on the PDF and hope the watermark doesn't screw with the process too much.
In the end, if you want a quick 'n easy fix, and can live with the watermark, use either PDFRasterfarian or PDFRead to convert to a more Reader-friendly version. With whatever you choose, Good luck!