How to produce a Graphviz PDF with smaller margins?

Graphviz is a great tool to generate graph images from a textual description.

The following tip shows how you can generate a PDF file with smaller margins.
The source file contains:

digraph G {
    margin=0;
    "subject" -> "object" [label="predicate"];
}

Alternatively, the margin can also be set in the command line:

> dot -Tpdf -Gmargin=0 triple.gv > triple.pdf