public bool Print()
{
try
{
PrintDocument docToPrint = new PrintDocument();
docToPrint.BeginPrint += DocToPrint_BeginPrint;
docToPrint.PrintPage += new System.Drawing.Printing.PrintPageEventHandler(this.docToPrint_PrintPage);
//docToPrint.DefaultPageSettings.Landscape = false;

            PaperSize p = null;
            foreach (PaperSize ps in docToPrint.PrinterSettings.PaperSizes)
            {
                if (ps.PaperName.Equals("102 x 152 毫米 (4 x 6 英寸)"))
                {
                    p = ps;
                    break;
                }
            }

            docToPrint.DefaultPageSettings.PaperSize = p;
            docToPrint.DefaultPageSettings.Margins = new Margins(1, 1, 1, 1);
            docToPrint.DefaultPageSettings.Color = true;//是否彩色
            //docToPrint.DefaultPageSettings.Landscape = true;

            docToPrint.PrinterSettings.DefaultPageSettings.PaperSize = p;
            docToPrint.PrinterSettings.DefaultPageSettings.Margins = new Margins(1, 1, 1, 1);
            docToPrint.PrinterSettings.DefaultPageSettings.Color = true;

            //System.Windows.Application.PrintDialog printDialog = new System.Windows.Forms.PrintDialog();
            //printDialog.AllowSomePages = true;
            //printDialog.ShowHelp = true;
            //printDialog.Document = docToPrint;
            //if (printDialog.ShowDialog() == DialogResult.OK)
            //{
            //    docToPrint.Print();
            //}

            docToPrint.Print();
            return true;
        }
        catch (Exception ex)
        {
            Log.WriteLog($"照片打印失败！异常原因：{ex.Message}");
            return false;
        }

    }

没有这个属性可以设置纸张类型的。