It is hard to read black letters on dark red background for my eyes...
Anyway, I will not look at the code.
Export to PDF (your subject should use lower case letters too!) is generally intended to export static images (or several pages, but I think it is out of this context).
I don't see a noLoop() in setup() nor an exit() call in draw(), so it will be called lot of times before you hit a key. Hence the many duplicates in the file. Since the drawings don't vary between each frame, just make the stop unconditional.
Note that you could have used the repetitive calls to draw() to replace your while loop, if you want to control when to stop.
See http://wiki.processing.org/w/Technical_FAQ

Note that if you want to export to 3D, you have a DXF renderer too.

Hi PhiLho,

1. There is exit command in void keyPressed().
2. If I write noLoop(); in setup I get error: missing a popMatrix() to go with that pushMatrix()..... (program is runned but it does not export the file);
3. How should I make "the stop unconditional"?

Thank you in advance.

import processing.pdf.*;

void setup() {
  size (400, 400);
  background(0);
  String id = str(hour())+"_"+(minute())+"_"+str(second());
  beginRecord(PDF, "img"+id+".pdf");
  noLoop();
}


void draw() {
  float i = 0;
  while (i<100) {
    noFill();
    stroke(100);
    strokeWeight(1);
    ellipse(width/2+i, height/2, 100+i*3, 100- i*5);
    i = i + 1;
  }
}


void keyPressed() {
  endRecord();
  exit();
  print("a");
}

"How should I make "the stop unconditional"?"
--> Just move the code from your keyPressed-function to the end of the draw-function. So after everything is drawn, the record is stopped.

1. I saw it, I wrote "in draw()"!
2. Yes, because you miss the endRecord(); exit(); in draw() too. The noLoop() isn't necessary actually, if you exit in draw().
3. As said above by benja, and in my 2.

And thanks for fixing the subject!

Thank  you Benja and PhiLho, it works:)