[noname120]

Have you considered using pandoc[1]?

  pandoc file1.md file2.md .... -o final.md

or

  pandoc file1.md file2.md .... -o final.pdf

[1] https://pandoc.org/

[dikei]

That's just concatenation though.

Asciidoctor has very good support for `include`, so you can include a file in the middle of another file. Furthermore, you can even do partial include where you only include a section of another the file in the current file.

I have setups where each of my files can work as a standalone document with proper Title and Appendix. These files can be compiled into another file where all the individual title are change to sub-title, and all the appendices are group together into one section.