Generate single-file HTML code documentation

I don't think there's an option that will produce the output as a single HTML file, but the RTF output may be suitable if you need an editable output format (I haven't tried this myself so I don't know how well this works).

If you want good quality printable output, then Doxygen can output LaTeX format (set GENERATE_LATEX to YES in your doxygen configuration file). This can then be converted to PDF, although you'll need to install a LaTeX distribution such as MiKTeX.

I think you can use HTMLDOC to convert the generated html files to a single html file. (I did not try it myself)

The manual includes the following example to generate a html from two source html files:

htmldoc --book -f output.html file1.html file2.html

But there is also a gui.