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The referenced post was about sections in PDF and user wanted to reorganize paragraphs of PDF Pages within PDF. As per our understandings, you want to re-order pages i.e. change the order of entire page in a PDF document. In order to achieve that, you may use following code snippet and in case you have any other requirements, please feel free to let us know.
Document doc = new Document(dataDir + "input.pdf");
Document finalDoc = new Document();
finalDoc.Save(dataDir + "output.pdf");