title: Merging PDF Files in Cocoa
body: <p>I would like to concatenate several PDF files to form one single PDF.
  Now I've come so far that I know, PDFKit is the proper way to go (I guess).
  But I am not sure, how to accomplish the merging. 
  Should I have one <code>PDFDocument</code> and several <code>PDFPage</code> and then call <code>insertPage</code> on the <code>PDFDocument</code> ?
  Or is there a much simpler way? I dont want to alter the PDFs contetwise, I just want to merge them.
  Thanks a lot!</p>