This is some build environment specific output. It shall help to identify problems during the build process.
You see this output because simplepdf_debug=True is set on the conf.py file.
Used Sphinx extension can be also found in the packages list of Python, which also includes the used version.
{% for x in spd.extensions %}
{{ x }}
{% endfor %}
This chapter shows a list of installed packages in the current Python environment, which was used to build this PDF. The second value is the version number.
{% set packages = pyd.get_packages()%} {% set vips = ['sphinx_simplepdf', 'sphinx', 'weasyprint', 'PIL', 'pillow'] %}
{% for x in packages|sort %}
{% if x in vips %}
{{ x }}: {{ packages[x] }}
{% endif %}
{% endfor %}
{% for x in packages|sort %}
{% if x not in vips%}
{{ x }}: {{ packages[x] }}
{% endif %}
{% endfor %}