Using Pandoc to generate PDFs from Markdown
on a Mac running macOS 10.13.4
To install the needed components you can use Homebrew

Two Components are needed:
Pandoc
PDFLaTex
Install instructions:
Use Homebrew to install pandoc:

brew install pandoc
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Then use Homebrew to install the PDFLaTex program.

brew install --cask basictex
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You should now have all the needed components but it won't work until the pdflatex executable is available in your PATH environment variable. To configure this my technique is to sym link the executable to a directory already in my PATH.

ln -s -v /Library/TeX/texbin/pdflatex /usr/local/bin/pdflatex
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Now if I enter which pdflatex on the command line the system responds:

/usr/local/bin/pdflatex

And now I'm able to generate a PDF from my Markdown file with this command:

pandoc file.md -s -o file.pdf