missing the comparison with poppler

[ousia]

@JorjMcKie,

in both about-feature-matrix.rst and about-performance.rst, I think it would be fine to include Poppler.

Just in case you might be inclined. Many thanks for all your work.

[ousia]

BTW, in app4.rst#tools-used, I think that having the version number of each tool is essential.