Class PageSettings

public class PageSettings
{
    public bool IsFirstPage { get; set; }
    public bool IsLastPage { get; set; }
}
Or if you prefer, maintaining existing line breaks for readability:
public class PageSettings
{
    public bool IsFirstPage { get; set; }
    public bool IsLastPage { get; set; }
}

string dataDir = RunExamples.GetDataDir_LoadingAndSaving();
   Document oneFile = new Document(dataDir + "OneNote.one");
   var dst = Path.Combine(dataDir, "SaveToPdfUsingLetterPageSettings.pdf");
   oneFile.Save(dst, new PdfSaveOptions() { PageSettings = PageSettings.Letter });

string dataDir = RunExamples.GetDataDir_LoadingAndSaving();
   Document oneFile = new Document(dataDir + "OneNote.one");
   var dst = Path.Combine(dataDir, "SaveToPdfUsingA4PageSettingsWithoutHeightLimit.pdf");
   oneFile.Save(dst, new PdfSaveOptions() { PageSettings = PageSettings.A4NoHeightLimit });

public static PageSettings A4
   {
      get
      {
         return new PageSettings
         {
            Orientation = Orientation.Portrait,
            PaperKind = PaperKind.A4,
            Margins = new MarginOptions
            {
               Left = 28,
               Right = 28,
               Top = 28,
               Bottom = 28
            }
         };
      }
   }

public static PageSettings A4NoHeightLimit
   {
      get
      {
         return new PageSettings
         {
            Orientation = Orientation.Portrait,
            PaperKind = PaperKind.A4,
            Margins = new MarginOptions
            {
               Left = 72,
               Right = 72,
               Top = 72,
               Bottom = 72
            },
            HeaderMargin = new MarginOptions { Left = 36, Right = 36 },
            FooterMargin = new MarginOptions { Left = 36, Right = 36 },
            HeaderDistance = 0,
            FooterDistance = 0,
            GutterDistance = 0,
            IsLandscape = false,
            StartPageNumber = 1,
            IsFirstPageIIDDefault = true,
            IsDifferentOddEvenHeadersFooters = false,
            IsMirrorMargins = false,
            IsApplyHeaderFooterAsTable = false
         };
      }
   }

string dataDir = RunExamples.GetDataDir_LoadingAndSaving();
   Document oneFile = new Document(dataDir + "OneNote.one");
   var dst = Path.Combine(dataDir, "SaveToPdfUsingA4PageSettingsWithoutHeightLimit.pdf");
   oneFile.Save(dst, new PdfSaveOptions { PageSettings = PageSettings.A4NoHeightLimit });

public static PageSettings Letter
   {
      get;
   }

string dataDir = RunExamples.GetDataDir_LoadingAndSaving();
   Document oneFile = new Document(dataDir + "OneNote.one");
   var dst = Path.Combine(dataDir, "SaveToPdfUsingLetterPageSettings.pdf");
   oneFile.Save(dst, new PdfSaveOptions { PageSettings = PageSettings.Letter });

public static PageSettings LetterNoHeightLimit
   {
      get;
   }