Compile markdown files with pandoc in shebang. Excute .md file as a script: "./Document.md". You might need to set the executable bit with chmod u+x Document.md

Document.md

#!/usr/bin/env -S bash -c 'pandoc --from markdown -V links-as-notes -V boxlinks -V pagestyle:empty --pdf-engine xelatex -V mainfont:'FiraSans-Medium' -V geometry:a6paper -t pdf -o "$(basename ${0} md)pdf" <(tail -n +2 "${0}")'

Dear reader,

This is a letter addressed to you, written in Markdown.

Author Name