That's a well-known problem: extracting things from a pdf-file doesn't necessarily result in something that's useful for further processing. That's not only for graphics, that's for MS Word also. Think about converting a .pdf to Excel. You won't get the formulas!
Consider a pdf-file as to be useful for presentation (view on screen, and print if allowed by the author).
So the two things you can do:
1. Ask the author of the pdf for the original processable file.
2. Make a screen print, save that as jpg or bmp and use your favorite photo-editor (even MS Paint is useful to change colors) to edit it.
No need to be desperate. Photo-editors can do quite a lot.
I am desperate. I'm trying to extract to extract a map from PDF file, save it as SVG and replace some colors (climate zones) by one color in the whole image, so that there is just one climate zone left. First I tried to use Inkscape. I extracted the map, saved it as svg file, BUT I can't replace any color (extensions - color - replace color). But it's worse. It doesn't display properly in any web browser. And I can't save it as PNG either, there's just one quarter of the image in the png file. Here is the map:
Original source from which I extracted it (last page):
I tried Corel Draw and Adobe Illustrator, but these 3 aren't even compatible, its incredible. Corel Draw doesn't work at all, Illustrator could be used for work from the very beginning, because it isnt compatible with Ikscape. But I don't know how to work with it.
Are you able to change the map in ANY vector editor in any way so that 1.) it will display properly in any web browser and 2.) I will be able to replace one color by another in the whole image?