HTMLDOC converts Hyper-Text Markup Language ("HTML") input files into
indexed HTML, Adobe(r) PostScript(r), or Adobe(r) Portable Document
Format ("PDF") files.
HTMLDOC supports most HTML 3.2 elements, some HTML 4.0 elements, and
can generate title and table of contents pages. The 1.8.x releases
do not support stylesheets.
HTMLDOC can be used as a standalone application, in a batch document
processing environment, or as a web-based report generation application.
No restrictions are placed upon the output produced by HTMLDOC.

htmldoc requires fltk (available on SlackBuilds.org).