The paper size option is available in PrintDocument
private void SetPaperSize()
{
int legalPaperIndex = 5;//See all types: http://msdn.microsoft.com/en-us/library/system.drawing.printing.papersize.rawkind.aspx
for (int i = 0; i < printDocument.PrinterSettings.PaperSizes.Count - 1; i++)
{
if (printDocument.PrinterSettings.PaperSizes[i].RawKind == legalPaperIndex)
{
printDocument.DefaultPageSettings.PaperSize = printDocument.PrinterSettings.PaperSizes[i];
}
}
}