The dot file is a textual file format used to represent graphs. The dot program, which ships with GraphViz, can be used to convert the dot file into file formats that help visualize the graph. Some of the supported output file formats include PNG, PS and Dia.
For example, to convert to PNG:
$ dot foo.dot -Tpng -o foo.png
Tried with: GraphViz 2.26.3-10ubuntu1 and Ubuntu 12.04 LTS