使用itext7而不是iTextSharp为pdf文档添加水印

using iText.Kernel.Pdf;
using iText.Layout;
using iText.Layout.Element;
using iText.Layout.Properties;

string inputFilePath = "input.pdf";  // 输入的 PDF 文件路径
string outputFilePath = "output.pdf";  // 输出的 PDF 文件路径
string watermarkText = "Confidential";  // 水印文本

PdfDocument pdfDoc = new PdfDocument(new PdfReader(inputFilePath), new PdfWriter(outputFilePath));
Document doc = new Document(pdfDoc);

// 创建水印元素
Paragraph watermark = new Paragraph(watermarkText)
    .SetFontColor(DeviceRgb.WHITE)
    .SetFontSize(60)
    .SetOpacity(0.3f)
    .SetRotationAngle(Math.PI / 4)
    .SetTextAlignment(TextAlignment.CENTER)
    .SetFixedPosition(100, 200, 400);

// 将水印添加到每一页
for (int i = 1; i <= pdfDoc.GetNumberOfPages(); i++)
{
    doc.ShowTextAligned(watermark, pdfDoc.GetPage(i).GetPageSize().GetWidth() / 2, pdfDoc.GetPage(i).GetPageSize().GetHeight() / 2, i, TextAlignment.CENTER, VerticalAlignment.MIDDLE, 45);
}

doc.Close();