Just to be clear, since I don't think I did a great job of explaining the problem:
I'm not trying to fix a watermark. The images literally have information written over them in a text layer (which is helpful in in every way except for the way that I actually need: to have just the image and not the text layer, without it clearly looking like I've doctored the image).
The PDF in question is for a tabletop RPG product. My gaming group uses a projector instead of a whiteboard or paper, and it's extremely frustrating trying to hand-draw maps to use for the projector. The PDF product is a bunch of maps for the group, except that the publisher brilliantly put the text spoiler information over the images in such a way that it can't be meaningfully used. I'm trying to save a lot of time hand-drawing every map image by exporting an image without the spoiler text.
Thanks in advance.
I'm using Adobe Reader 9...
You may try Adobe Acrobat.
Reader will not do what you are looking for, and I doubt the third party software will either.
Do you have Illustrator?
If so there might be a chance it will do what you want......removing the text & leaving image alone.