HTMLDOC converts HTML source files into indexed HTML, PostScript, or
Portable Document Format (PDF) files that can be viewed online or
printed. With no options a HTML document is produced on stdout.
The second form of HTMLDOC reads HTML source from stdin, which allows
you to use HTMLDOC as a filter.
The third form of HTMLDOC launches a graphical interface that allows
you to change options and generate documents interactively.