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 });
            }
        }
    }