EmbedPdeInPdf.pde

import java.util.Arrays;

class EmbedPdeInPdf {
  PApplet parent;
  String filename;
  
  EmbedPdeInPdf(PApplet _parent) {
    parent = _parent;
  }
  
  void beginRecord(String mode, String filename) {
    parent.beginRecord(mode, filename);
    this.filename = filename;
  }

  void endRecord() {
    parent.endRecord();
    
    String[] pdefiles = new File(sketchPath).list();
    
    byte[] pdf = loadBytes(this.filename);
    ArrayList<Byte> export = new ArrayList<Byte>();
    
    export.addAll(Arrays.asList(new Byte[] {0x2F, 0x2A, 0x0A}));
    for (byte b : pdf) {
      export.add(b);
    }
    export.addAll(Arrays.asList(new Byte[] {0x0A, 0x2A, 0x2F, 0x0A}));
    
    for (String pdefile : pdefiles) {
      if (pdefile.indexOf(".pde") != pdefile.length() - ".pde".length()) {
        continue;
      }
      
      byte[] pde = loadBytes(pdefile);
      for (byte b : pde) {
        export.add(b);
      }
      export.add((byte)0x0A);
    }
    
    byte[] exportArray = new byte[export.size()];
    for (int i = 0; i < exportArray.length; i++) {
      Byte b = export.get(i);
      exportArray[i] = b.byteValue();
    }

    saveBytes(this.filename, exportArray);
  }
}

Example.pde

import processing.pdf.*;

EmbedPdeInPdf pdf;

void setup() {
  size(400, 400);
  noLoop();
  pdf = new EmbedPdeInPdf(this);
  pdf.beginRecord(PDF, "export.pdf");
}

void draw() {
  background(128);
  ellipse(width/2, height/2, width/2, height/2);

  pdf.endRecord();
}