title: Best way to change pagination of existing PDF
body: <p>We have a PDF that is generated as A5 landscape pages.
  With that, we need to do a PDF with A4 portrait page format, by putting 2 pages of the source PDF on top of each other on each page of the result PDF.</p>
  
  <p>Do you know a good library that could do that kind of PDF manipulations ? This should happen server side from an ASP.NET web application, with as little to deploy on the server as possible.</p>