紧急求助：使用iTextSharp删除已加PDF水印

leon51 2020-07-09 10:22:20

我需要给pdf加上水印，重新添加时需先删除已加的水印，每次添加的水印可能是不一样的。
网上说加水印有很多种方法，我找到其中以下两种并测试ok。
想当然地认为自已加的，能加就能删除，但没有找到删除上次已加的水印的方法，因为已加的图层不知如何获取，每次的水印内容又不一样。

第一种加水印的方式

PdfReader reader1 = new PdfReader(startFile);

using (FileStream fs = new FileStream(watermarkedFile, FileMode.Create, FileAccess.Write, FileShare.None))

{

	using (PdfStamper stamper = new PdfStamper(reader1, fs))

	{

		int pageCount1 = reader1.NumberOfPages;

		PdfLayer layer = new PdfLayer("WatermarkLayer", stamper.Writer);

		for (int i = 1; i <= pageCount1; i++)

		{

			iTextSharp.text.Rectangle rect = reader1.GetPageSize(i);

			PdfContentByte cb = stamper.GetUnderContent(i);

			cb.BeginLayer(layer);

			cb.SetFontAndSize(BaseFont.CreateFont(BaseFont.HELVETICA, BaseFont.CP1252, BaseFont.NOT_EMBEDDED), 50);

			PdfGState gState = new PdfGState();

			gState.FillOpacity = 0.25f;

			cb.SetGState(gState);

			cb.SetColorFill(BaseColor.BLACK);

			cb.BeginText();

			cb.ShowTextAligned(PdfContentByte.ALIGN_CENTER, watermarkText, rect.Width / 2, rect.Height / 2, 45f);

			cb.EndText();

			cb.EndLayer();

		}

	}

}

第二种加水印的方式

PdfReader pdfReader = null;

PdfStamper pdfStamper = null;

pdfReader = new PdfReader(inputfilepath);

pdfStamper = new PdfStamper(pdfReader, new FileStream(outputfilepath, FileMode.OpenOrCreate));

int total = pdfReader.NumberOfPages + 1;

Rectangle psize = pdfReader.GetPageSize(1);

float width = psize.Width;

float height = psize.Height;

PdfContentByte content;

BaseFont font = BaseFont.CreateFont(BaseFont.TIMES_ROMAN, BaseFont.CP1252, false);



PdfGState gs = new PdfGState();

for (int i = 1; i < total; i++)

{

	content = pdfStamper.GetOverContent(i);

	gs.FillOpacity = 0.3f;

	content.SetGState(gs);

	content.BeginText();

	content.SetColorFill(BaseColor.RED);

	content.SetFontAndSize(font, 30);

	content.SetTextMatrix(0, 0);

	content.ShowTextAligned(Element.ALIGN_LEFT, waterMarkName, 10, height - 30, 0);

	content.EndText();

}