Undefined control sequency in \documentclass?

Hello I'm running TexWorks from the MiKTeX & consistently getting this error:

! Undefined control sequence.
l.6 \documentclass
                  [prd,12pt,reprint,showkeys,showpacs,nofootinbib]{revtex4-1}
? 

Here is my whole preamble:

\documentclass[prd,12pt,reprint,showkeys,showpacs,nofootinbib]{revtex4-1}

%additional macros
\usepackage{amsmath} % for creating subequations
\usepackage{graphicx} % for insterting figures
\usepackage{verbatim} % for including verbatim text
\usepackage{color} % for colored text
\usepackage{subfigure} % for side-by-side figures
\usepackage{hyperref} % for creating hypertext links