Announcing pandoc-include-plus: A pandoc filter which supports "include" files. Included files can include other files, recursively. Paths to images are adjusted as needed to ensure that everything "just works". An option is provided to promote or demote heading levels in included files.

At the moment, only Markdown files can be included. However, I expect soon to be able to support all filetypes that Pandoc supports.

It is available either from Hackage, or as  Nix flake.

Hackage: https://hackage.haskell.org/package/pandoc-include-plus
Repo: https://codeberg.org/mhwombat/pandoc-include-plus