the pdf library can not render unicode characters, for example, greek letters.
Code tested:

import processing.pdf.*;
size(600,800);
background(255);
beginRecord(PDF,"test.pdf");
PFont arial = createFont("Arial",48);
textFont(arial);
textSize(10);
fill(0);
text("\u03B1",50,50);
text("\u0391",50,70);
endRecord();

i can see the letters in the screen, but get an empty PDF file.
processing version:0135beta.

*** Bug 728 has been marked as a duplicate of this bug. ***

huh, that's interesting. i'm stumped actually, i could have sworn that i've
had unicode characters working just fine for me with the pdf library. we
may need an updated version of itext.

Looking into this today... It appears that the problem only occurs when
beginRecord() is in use. If you use PDF as the renderer, it writes the
characters just fine.

import processing.pdf.*;
size(800, 600, PDF, "test.pdf");
textMode(SHAPE);
background(255);
PFont arial = createFont("Arial", 48);
textFont(arial);
textSize(10);
fill(0);
text("testing?",100,50);
text("\u03B1",50,50);
text("\u0391",50,70);
line(20, 20, 80, 80);
exit();

Also, if you use textMode(SHAPE), it also works fine with beginRecord().
PGraphics p = beginRecord(PDF, "test.pdf");
p.textMode(SHAPE);
// the rest of the program

oops, that last comment was not quite correct; size(..., PDF) does not
work, only textMode(SHAPE) gets around the problem. (the first example
still had textMode(SHAPE) listed in it).

the problem here appears to be that the pdf library is not setting the font
correctly when createFont() is in use. (which makes it a higher priority
bug after all.)