public class PdfWriter
{
        /** A viewer preference */
        public const int PageLayoutSinglePage = 1;
        /** A viewer preference */
        public const int PageLayoutOneColumn = 2;
        /** A viewer preference */
        public const int PageLayoutTwoColumnLeft = 4;
        /** A viewer preference */
        public const int PageLayoutTwoColumnRight = 8;
        /** A viewer preference */
        public const int PageLayoutTwoPageLeft = 16;
        /** A viewer preference */
        public const int PageLayoutTwoPageRight = 32;

        // page mode (section 13.1.2 of "iText in Action")
        
        /** A viewer preference */
        public const int PageModeUseNone = 64;
        /** A viewer preference */
        public const int PageModeUseOutlines = 128;
        /** A viewer preference */
        public const int PageModeUseThumbs = 256;
        /** A viewer preference */
        public const int PageModeFullScreen = 512;
        /** A viewer preference */
        public const int PageModeUseOC = 1024;
        /** A viewer preference */
        public const int PageModeUseAttachments = 2048;

        //...
        //...
}

public enum ViewerPageLayout
{
     SinglePage = 1,
     OneColumn = 2,
     TwoColumnLeft = 4,
     TwoColumnRight = 8,
     TwoPageLeft = 16,
     TwoPageRight = 32
}