PDF and trojan

Recently, I read a news about that there is PDF flaw. I am not sure how is it happened. But you can read a news about this PDF and trojan problem:
http://www.eweek.com/article2/0,1759,2205400,00.asp?kc=EWRSS03119TX1K0000594

Beware of the PDF file when you receive a spam mail. The PDF file will disable the Windows Firewall, and download the trojan file.

I also read an article talk about that some people like to run the Windows with reduced rights (non-administrator rights). Because this can disallow the modification of you Windows system, such as installing unwanted programs.
http://www.techsupportalert.com/how_to_easily_run_programs_with_reduced_rights.htm