向PDF添加水印

在将Excel文件转换为PDF时，可能需要在PDF文件中添加水印。以下示例展示了在呈现PDF时如何向PDF添加文本和图像水印。

向PDF添加文本水印

通过指定文本和相应的字体，您可以轻松地向PDF添加文本水印。 您还可以在RenderingWatermark中设置对齐，偏移量，旋转，不透明度，前景/背景和在页面上的比例。

//prepare a workbook with 3 pages.
Workbook wb = new Workbook();
wb.Worksheets[0].Cells["A1"].PutValue("Page1");
int index = wb.Worksheets.Add();
wb.Worksheets[index].Cells["A1"].PutValue("Page2");
index = wb.Worksheets.Add();
wb.Worksheets[index].Cells["A1"].PutValue("Page3");
wb.Worksheets[index].PageSetup.PaperSize = PaperSizeType.PaperA3;

//create a font for watermark, and specify bold, italic, color.
RenderingFont font = new RenderingFont("Calibri", 68);
font.Italic = true;
font.Bold = true;
font.Color = Color.Blue;

//create a watermark from text and the specified font.
RenderingWatermark watermark = new RenderingWatermark("Watermark", font);

//specify horizontal and vertical alignment
watermark.HAlignment = TextAlignmentType.Center;
watermark.VAlignment = TextAlignmentType.Center;

//specify rotation
watermark.Rotation = 30;

//specify opacity
watermark.Opacity = 0.6f;

//specify the scale to page(e.g. 100, 50) in percent.
watermark.ScaleToPagePercent = 50;

//spcify watermark for rendering to pdf.
PdfSaveOptions options = new PdfSaveOptions();
options.Watermark = watermark;

wb.Save("output_text_watermark.pdf", options);

向PDF添加图像水印

您只需指定图像的图像字节，就可以向PDF添加图像水印。 您还可以在RenderingWatermark中设置对齐，偏移量，旋转，不透明度，前景/背景和在页面上的比例。

//prepare a workbook with 3 pages.
Workbook wb = new Workbook();
wb.Worksheets[0].Cells["A1"].PutValue("Page1");
int index = wb.Worksheets.Add();
wb.Worksheets[index].Cells["A1"].PutValue("Page2");
index = wb.Worksheets.Add();
wb.Worksheets[index].Cells["A1"].PutValue("Page3");
wb.Worksheets[index].PageSetup.PaperSize = PaperSizeType.PaperA3;

//create a watermark from image(you need to prepare image bytes).
byte[] imageBytes = null;
RenderingWatermark watermark = new RenderingWatermark(imageBytes);

//specify offset to alignment.
watermark.OffsetX = 100;
watermark.OffsetY = 200;

//specify rotation
watermark.Rotation = 30;

//specify watermark to background.
watermark.IsBackground= true;

//specify opacity
watermark.Opacity = 0.6f;

//specify the scale to page(e.g. 100, 50) in percent.
watermark.ScaleToPagePercent = 50;

//spcify watermark for rendering to pdf.
PdfSaveOptions options = new PdfSaveOptions();
options.Watermark = watermark;

wb.Save("oputput_image_watermark.pdf", options);