PDF .Net

using System;
using System.IO;
using SautinSoft;
using SautinSoft.Pdf;

namespace Sample
{
    class Sample
    {
        static void Main(string[] args)
        {
            // Load an existing PDF document
            PdfDocument document = new PdfDocument();
            document.Load("input.pdf");
            // Rotate the first page by 90 degrees
            PdfPage page = document.Pages[0];
            page.Rotation = PdfRotation.Rotate90;
            // Save the modified document
            document.Save("output.pdf");
            // Open the modified document
            System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo("output.pdf") { UseShellExecute = true });
        }
    }
}