Lagging when viewing PDFs with Lion

I just bought a Macbook Pro 15 and installed Lion yesterday. Everything was great until I opened a PDF file, which isnt too big in size, around 5mb. Scrolling was extremely laggy and patchy and isnt smooth as it should be, there is also significant lag when I try to expand the PDF. I am unsure what the problem is cuz absolutely everything else runs extremely slowly, and i tried different readers (including Preview) and the PDFs lag in every single program. I tried looking this problem up on different forums and people have experienced this problem before but it doesnt seem there is a clear solution. I'd appreciate it if anyone could give me some help on this. Thanks!