I wonder why okular is very slow when I am trying to open a big pdf with a lot of images. I download The emerald city of Oz pdf from here
Then I tried to open it with Okular, xpdf, acrobat reader, and SumatraPDF (under wine) and I got this statistics:

Program CPU% Memory

Okular 51% 247M
Xpdf 50% 263M
SumatraPDF 51% 247M
acrobat 49% 70M

You can see that Okular using a lot of memory. I have to wait a few seconds to see the next page in the pdf.

I am using Kubuntu 10.10 and my laptop is ThinkPad T400.

Because the images are bitmaps rather than vector images - so they take a lot longer to download and unpack.