public void SplitDocument()
{
    //Initialize the SDK library
    //You have to call this function before you can call any PDF processing functions.
    PdfCommon.Initialize();

    //Open and load a PDF document from a file.
    using (var sourceDoc = PdfDocument.Load(@"c:\test001.pdf"))
    {
        //Create one PDF document for pages 1-5.
        using (var doc = PdfDocument.CreateNew())
        {
            //Import pages from source document
            doc.Pages.ImportPages(sourceDoc, "1-5", 0);
            //And save it to doc1.pdf
            doc.Save(@"c:\doc1.pdf", SaveFlags.Incremental);
        }

        //Create another PDF document for pages 5-10.
        using (var doc = PdfDocument.CreateNew())
        {
            //Also import pages
            doc.Pages.ImportPages(sourceDoc, "5-10", 0);
            //And save them too
            doc.Save(@"c:\doc2.pdf", SaveFlags.Incremental);
        }
    }
    //Release all resources allocated by the SDK library
    PdfCommon.Release();
}