Description:
The lesspipe package lists html2text as an optional dependency. The only package in the standard repos that provide html2text is python-html2text.
This version of html2text does not work with lesspipe as it uses a different syntax and breaks lesspipe, see [1]. In fact many programs have converged on the name html2text.
The problem arises from the fact that lesspipe only searches for an executable with the name html2text.

A proposed fix would be to remove the optional dependency on html2text and replace it with one of the other alternatives:
(1) lynx
(2) w3m
(3) elinks
(4) links
all of which are provided in the standard repositories, and add a conflict with python-html2text.
As is stands now html2text is the first program tried by lesspipe and causes it to fail.

There will still be a lingering problem if a user has none of the above but (a wrong) html2text installed as the presence of html2text enables html parsing.
See the upstram bug report [1] for more information on this. My proposed patch [2] tries to enable a workaround for this specific issue.

To partially remedy this at the moment you could change line 419 to 'html2text<TAB>N' and use the --fixed option for building.
Another approach would be to patch lesspipe.sh.in with the correct syntax for the provided html2text.

The intended html2text can be found here [4]. I have written a PKGBUILD for this version and could upload this to the AUR if this is required (I attach the PKGBUILD for now).


Additional info:
[1] The forum discussion revealing this: https://bbs.archlinux.org/viewtopic.php?id=270122
[2] upstream bug report: https://github.com/wofr06/lesspipe/issues/60
[3] upstram patch proposal: https://github.com/wofr06/lesspipe/pull/63
[4] https://github.com/grobian/html2text

Steps to reproduce:
install lesspipe and python-html2text
lesspipe.sh some.pdf