How can I create plaintext files with Markdown syntax and convert them to PDF format? I am very much a novice at this, so please bear with me.

I'm intrigued by the idea of using Markdown. I want to be able to write my stuff in a plaintext editor on OS X and iOS and save it in Dropbox in .txt format using a Markdown syntax. I don't want to save my files in markdown format but as plain text. I need support for footnotes, so the Multimarkdown syntax seems like an obvious option.

What tools can I use on OS X and iOS to convert my .txt files, marked up with a Markdown syntax, to .pdf format? Is this even possible?

Thanks for reading.
I use Marked to process text files to pdf routinely.

No matter what editor you use, Marked will open and re-save a PDF generated from the plain text input by opening and re-saving the file. 

It also saves to HTML or RDF output from markdown.

In reality, any program that renders markdown could print to PDF using OS X core services (File -> Print -> PDF -> Save as PDF), but I much prefer having Marked for it's multitude of handy and flexible processing options and it's ability to live preview markdown files as I edit them in another editor:


Printing: TOC, suppressing link underline colors, better page breaks
Multiple styles of markdown rendering
Support for custom processors, all manner of smart (and dumb) typography
overall clean, fast, robust, elegant software for a very reasonable price