<a href="#" onclick="window.open('MyPDF.pdf', '_blank', 'fullscreen=yes'); return false;">MyPDF</a>

The above link will open the PDF in full screen mode, that's the best you can achieve.

var pdf = MyPdf.pdf;
window.open(pdf);

This will open the pdf document in a full window from JavaScript

A function to open windows would look like this:

function openPDF(pdf){
  window.open(pdf);
  return false;
}

I'm going to take a chance here and actually advise against this. I suspect that people wanting to view your PDFs will already have their viewers set up the way they want, and will not take kindly to you taking that choice away from them :-)

Why not just stream down the content with the correct content specifier?

That way, newbies will get whatever their browser developer has a a useful default, and those of us that know how to configure such things will see it as we want to.