从PDF中删除水印

Question

我用过第一个代码创建一个水印并删除它并且它完美无缺

    private void Form1_Load(object sender, EventArgs e) {
        string workingFolder = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
        string startFile = Path.Combine(workingFolder, "StartFile.pdf");
        string watermarkedFile = Path.Combine(workingFolder, "Watermarked.pdf");
        string unwatermarkedFile = Path.Combine(workingFolder, "Un-watermarked.pdf");
        string watermarkText = "This is a test";

        //SECTION 1
        //Create a 5 page PDF, nothing special here
        using (FileStream fs = new FileStream(startFile, FileMode.Create, FileAccess.Write, FileShare.None)) {
            using (Document doc = new Document(PageSize.LETTER)) {
                using (PdfWriter witier = PdfWriter.GetInstance(doc, fs)) {
                    doc.Open();

                    for (int i = 1; i <= 5; i++) {
                        doc.NewPage();
                        doc.Add(new Paragraph(String.Format("This is page {0}", i)));
                    }

                    doc.Close();
                }
            }
        }

        //SECTION 2
        //Create our watermark on a separate layer. The only different here is that we are adding the watermark to a PdfLayer which is an OCG or Optional Content Group
        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;
                //Create a new layer
                PdfLayer layer = new PdfLayer("WatermarkLayer", stamper.Writer);
                for (int i = 1; i <= pageCount1; i++) {
                    iTextSharp.text.Rectangle rect = reader1.GetPageSize(i);
                    //Get the ContentByte object
                    PdfContentByte cb = stamper.GetUnderContent(i);
                    //Tell the CB that the next commands should be "bound" to this new layer
                    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();
                    //"Close" the layer
                    cb.EndLayer();
                }
            }
        }

        //SECTION 3
        //Remove the layer created above
        //First we bind a reader to the watermarked file, then strip out a bunch of things, and finally use a simple stamper to write out the edited reader
        PdfReader reader2 = new PdfReader(watermarkedFile);

        //NOTE, This will destroy all layers in the document, only use if you don't have additional layers
        //Remove the OCG group completely from the document.
        //reader2.Catalog.Remove(PdfName.OCPROPERTIES);

        //Clean up the reader, optional
        reader2.RemoveUnusedObjects();

        //Placeholder variables
        PRStream stream;
        String content;
        PdfDictionary page;
        PdfArray contentarray;

        //Get the page count
        int pageCount2 = reader2.NumberOfPages;
        //Loop through each page
        for (int i = 1; i <= pageCount2; i++) {
            //Get the page
            page = reader2.GetPageN(i);
            //Get the raw content
            contentarray = page.GetAsArray(PdfName.CONTENTS);
            if (contentarray != null) {
                //Loop through content
                for (int j = 0; j < contentarray.Size; j++) {
                    //Get the raw byte stream
                    stream = (PRStream)contentarray.GetAsStream(j);
                    //Convert to a string. NOTE, you might need a different encoding here
                    content = System.Text.Encoding.ASCII.GetString(PdfReader.GetStreamBytes(stream));
                    //Look for the OCG token in the stream as well as our watermarked text
                    if (content.IndexOf("/OC") >= 0 && content.IndexOf(watermarkText) >= 0) {
                        //Remove it by giving it zero length and zero data
                        stream.Put(PdfName.LENGTH, new PdfNumber(0));
                        stream.SetData(new byte[0]);
                    }
                }
            }
        }

        //Write the content out
        using (FileStream fs = new FileStream(unwatermarkedFile, FileMode.Create, FileAccess.Write, FileShare.None)) {
            using (PdfStamper stamper = new PdfStamper(reader2, fs)) {

            }
        }
        this.Close();
    }
}

}

但是当我使用数字签名的某个时候，当我试图删除水印时，某些页面丢失了信息，我们想要使用PdfLayerRemover并改为C＃但是当我做了这个

 PdfDictionary ocProps = _reader.Catalog.GetAsDict(PdfName.OCPROPERTIES); 

我曾经使用过第一个代码创建一个水印并删除并且它工作得很完美但是当我使用数字签名时我试图删除水印时某些页面丢失了信息，他们我想要使用PdfLayerRemover我改为C＃，但是当我做了这个

PdfDictionary ocProps = _reader.Catalog.GetAsDict（PdfName.OCPROPERTIES）;

总是得到空值，pdf有水印???请问如果可以帮助我和pdf有ocpproperties因为当我使用这个工作，但它删除了其他信息。但是Itextshap版本5.5.2.0的方式

if (content.IndexOf("/OC") >= 0 && content.IndexOf(watermarkText) >= 0) {
                    //Remove it by giving it zero length and zero data
                    stream.Put(PdfName.LENGTH, new PdfNumber(0));
                    stream.SetData(new byte[0]);

                }