You don't have to buy the whole suite, but you can't buy CS4 or CS5. They are no longer sold by Adobe.
You can buy CS6.
But check carefully that your hardware and operating system can run CS6.
However, you might want to use this forum to troubleshoot what problems you're having creating PDF files.
Thanks Sandee... I had a feeling this would be the case and I'm not sure I can run CS6 on my "vintage" iMac (as it has been called)...so I guess this is going to be an expensive year!