mdtopdf() {
     filename="${1%.*}"
     pandoc -t html $filename.md -o $filename.pdf
}

mdtopdf() {
     filename="${1%.*}"
     pandoc -t html --css /path/to/custom.css $filename.md -o $filename.pdf
}

$ mdtopdf sample.md

[WARNING] This document format requires a nonempty <title> element.
  Please specify either 'title' or 'pagetitle' in the metadata,
  e.g. by using --metadata pagetitle="..." on the command line.
  Falling back to 'sample'
Loading page (1/2)
Printing pages (2/2)                                               
Done