linuxdoc-tools binary package in Ubuntu Focal arm64

 LinuxDoc sgml is a highly configurable text format for writing
 documentation, something like html only it's simpler and can be
 converted to various other formats, including html for websites.
 You write a LinuxDoc document using any text editor such as vim.
 Then you use linuxdoc-tools to convert it to html, rtf, plain-text
 (install linuxdoc-tools-text), info (install linuxdoc-tools-info),
 LaTeX, dvi or postscript (install linuxdoc-tools-latex). The
 sgmltools-lite package can convert LinuxDoc to DocBook format.
 .
 LinuxDoc can automatically create a table of contents. It's easier to
 write and read than DocBook since it allows one to omit most closing
 tags while paragraphs are separated by just blank lines.

Source package