这段代码中使用了((Sheet) cell).getDrawingPatriarch()来获取单元格中图片的绘图区域对象，但是这里的cell实际上应该是一个Picture类型的单元格。所以需要修改成(HSSFPicture)cell来获取绘图区域对象。

另外，在处理图片时，可以使用POI提供的API来获取图片数据和MIME类型，而不是直接从单元格中读取。因为可能会存在一些特殊情况下无法正确读取图片数据的问题。

优化后的代码如下：

import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import javax.imageio.ImageIO;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;
import com.itextpdf.text.BadElementException;
import com.itextpdf.text.Document;
import com.itextpdf.text.Element;
import com.itextpdf.text.Font;
import com.itextpdf.text.Image;
import com.itextpdf.text.Paragraph;
import com.itextpdf.text.Rectangle;
import com.itextpdf.text.pdf.PdfPCell;
import com.itextpdf.text.pdf.PdfWriter;
public class ExcelToPdfConverter {
    public static void main(String[] args) throws Exception {
        // Read the Excel file
        FileInputStream inputStream = new FileInputStream(new File("C:\\Users\\hspcadmin\\Desktop\\测试\\秦皇岛银行资管系统对接ECIF测试案例.xls"));
        Workbook workbook = new HSSFWorkbook(inputStream);
        Sheet sheet = workbook.getSheetAt(0);
        // Create the PDF document
        Document document = new Document();
        PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream(new File("C:\\Users\\hspcadmin\\Desktop\\测试\\output.pdf")));
        document.open();
        // Set up fonts for the PDF document
        Font titleFont = new Font(Font.FontFamily.TIMES_ROMAN, 16, Font.BOLD);
        Font headerFont = new Font(Font.FontFamily.HELVETICA, 12, Font.BOLD);
        Font cellFont = new Font(Font.FontFamily.COURIER, 10);
        // Process the Excel data
        for (int i=0; i<sheet.getLastRowNum()+1; i++) {
            Row row = sheet.getRow(i);
            if (row == null) {
                continue;  // skip blank rows
            }
            PdfPTable table = new PdfPTable(row.getLastCellNum());
            table.setWidthPercentage(100);
            for (int j=0; j<row.getLastCellNum(); j++) {
                Cell cell = row.getCell(j);
                if (cell == null) {
                    PdfPCell pdfCell = new PdfPCell();
                    pdfCell.addElement(new Paragraph("", cellFont));
                    table.addCell(pdfCell);
                    continue;  // skip blank cells
                }
                PdfPCell pdfCell = new PdfPCell();
                switch (cell.getCellTypeEnum()) {
                    case STRING:
                        String value = cell.getStringCellValue();
                        Paragraph paragraph = new Paragraph(value, cellFont);
                        pdfCell.addElement(paragraph);
                        break;
                    case NUMERIC:
                        double numericValue = cell.getNumericCellValue();
                        Paragraph numericParagraph = new Paragraph(Double.toString(numericValue), cellFont);
                        pdfCell.addElement(numericParagraph);
                        break;
                    case BOOLEAN:
                        boolean boolValue = cell.getBooleanCellValue();
                        Paragraph boolParagraph = new Paragraph(Boolean.toString(boolValue), cellFont);
                        pdfCell.addElement(boolParagraph);
                        break;
                    case FORMULA:
                        if (cell.getCachedFormulaResultTypeEnum() == CellType.STRING) {
                            String formulaValue = cell.getStringCellValue();
                            Paragraph formulaParagraph = new Paragraph(formulaValue, cellFont);
                            pdfCell.addElement(formulaParagraph);
                        } else if (cell.getCachedFormulaResultTypeEnum() == CellType.NUMERIC) {
                            double formulaNumericValue = cell.getNumericCellValue();
                            Paragraph formulaNumericParagraph = new Paragraph(Double.toString(formulaNumericValue),
                                    cellFont);
                            pdfCell.addElement(formulaNumericParagraph);
                        }
                        break;
                    case BLANK:
                         // Do nothing
                         break;
                    default: 
                       // Handle all other cases using the same approach as above
                       String otherValue=cell.getStringCellValue();  
                       Paragraph otherPara=new Paragraph(otherValue,cellFont);  
                       pdfCell.addElement(otherPara);   
                }
                table.addCell(pdfCell);
                // Handle images separately using ImageIO library
                if (cell.getCellTypeEnum() == CellType.PICTURE && ((HSSFPicture)cell).getPictureData().getData() != null) {
                    byte[] pictureData = workbook.getAllPictures().get(((HSSFPicture)cell).getPictureIndex()-1).getData();
                    InputStream inputStream = new ByteArrayInputStream(pictureData);
                    BufferedImage image = ImageIO.read(inputStream);
                    Image img = getImageFromBufferedImage(image);
                    PdfPCell imageCell = getPdfPCellFromImage(img);
                    table.addCell(imageCell);
                }
            }
            // Add the table to the PDF document
            document.add(table);
        }
        // Save the PDF document
        document.close();
    }
    // 从BufferedImage获取iText中的Image
    private static Image getImageFromBufferedImage(BufferedImage image) throws BadElementException, IOException {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ImageIO.write(image, "png", baos);
        byte[] imageData = baos.toByteArray();
        return Image.getInstance(imageData);
    }
    // 从Image获取PdfPCell，设置单元格属性和样式
    private static PdfPCell getPdfPCellFromImage(Image img) {
        PdfPCell cell = new PdfPCell(img, true);
        cell.setHorizontalAlignment(Element.ALIGN_CENTER); // 设置水平居中
        cell.setVerticalAlignment(Element.ALIGN_MIDDLE); // 设置垂直居中
        cell.setBorder(Rectangle.NO_BORDER); // 去除边框线条
        return cell;
    }
}