On: How I Write Invoices in Vim

[semi-extrinsic]

For rendering markdown straight into PDF (and other formats), have a look at pandoc, it's really powerful. If you can make your markdown flavour compatible with (or a superset of) pandoc markdown it should be simple. See RMarkdown for inspiration.

[tambourine_man → semi-extrinsic]

Pandoc is great, but my layout is a bit complex, and last I checked, templating in HTML first seemed easier.