import processing.pdf.*;

boolean isMakingPdf = false;

void setup(){
}

void draw(){
  if(isMakingPdf){
     beginRecord(PDF, "frame-####.pdf");
  }

  //draw stuff

  if(isMakingPdf){
    endRecord();
    isMakingPdf = false;// stop pdf creation after the frame ends
  }
}

void keyPressed(){
//save PDF when you hit the o key
   if(key == 'o'){
     isMakingPdf = true;
   }

//save jpg image when you hit the s key
   if(key == 's'){
     saveFrame("frame-####.jpg");
   }
}

This is an slightly more involved processing basic sketch I use when creating Imagery so I can save and output images at any point in time when the sketch is running.

Basic Processing Sketch for Image making/experimentation

image

Processing