Not sure if it's a bug, but if you create a font (e.g. Arial) via the Processing interface, and use loadFont() rather than createFont() it seems to work fine (and that's the recommended approach when distributing sketches).  Oddly it works fine with both approaches when drawing a line on the 'descent' :/

I checked and with loadFont() it goes good and with createFont() not so i can assume that that is a bug right?

here:

font = loadFont("ArialMT-32.vlw"); //23.0
font = createFont("ArialMT", 32); //29.0

the 23.0 and 29.0 is the Ascent information

I wouldn't rush into filing a bug report...  I don't know enough about what createFont() or ascent() do internally to say for sure; but there might be valid explanations for this behaviour :/

I think this issue might give some answers.

Even if your problem isn't related to PDF the diff between bitmap and vector font might be the problem.

The default renderer which is JAVA2D use the native version of the font (vector).
If you change the renderer for P2D, textAscent() works.

In the todo.txt, there's a line " what's the difference with ascent on loadFont vs. createFont?" so i assume the dev team is aware of the problem.

What's strange is that from the procesing PGraphics source textAscent is computed this way :

1. return textFont.ascent() * ((textMode == SCREEN) ? textFont.size : textSize);

And this method is overloaded by PGraphicsJAVA2D. So i assume there is a problem in the overloaded PGraphicsJAVA2D testAscent() method.
This code produce strange result  :       

1. PFont font = createFont("Arial", 64);
2. textFont(font);
3. textSize(128);
4. println("TextSize :" + g.textSize + " ascent :" + g.textFont.ascent());
5. println("textAscent formula : " + (g.textSize*g.textFont.ascent()));
6. println("textAscent() :" + textAscent());

Output :

1. TextSize :128.0 ascent :0.71875
2. ascent() : 92.0
3. textAscent() :118.0

This :

1. size(100, 100, P2D);
2. PFont font = createFont("Arial", 64);
3. textFont(font);
4. textSize(128);
5. println("TextSize :" + g.textSize + " ascent :" + g.textFont.ascent());
6. println("textAscent formula : " + (g.textSize*g.textFont.ascent()));
7. println("textAscent() :" + textAscent())

Output a good result:

1. TextSize :128.0 ascent :0.71875
2. textAscent formula : 92.0
3. textAscent() :92.0

I tried the above code with pre-release rev0191 and this issue is fixed :

1. PFont font;
2. font = createFont("Arial", 64);
3. textFont(font);
4. textSize(128);
5. println(textAscent());

Output 92.0 which is correct.

pre-release rev0191 for the win!
Not for this (yeah also) but text drawned using floats gets much more the sizes you expect.
Hope there wll be a official release soon.