如何使用Apache PDFBox替换或删除pdf文件中的文本

Question

我需要更改PDF文档中的现有文本。我正在尝试使用Apache PDFBox删除并替换PDF文件中的某些文本，但它无法正常工作。

  doc = PDDocument.load("D://out.pdf"); //Input PDF File Name
    List pages = doc.getDocumentCatalog().getAllPages();
    for (int i = 0; i < pages.size(); i++)
    {
        PDPage page = (PDPage) pages.get(i);
        PDStream contents = page.getContents();
        PDFStreamParser parser = new PDFStreamParser(contents.getStream());
        parser.parse();
        List tokens = parser.getTokens();
        for (int j = 0; j < tokens.size(); j++)
        {
            Object next = tokens.get(j);
            if (next instanceof PDFOperator)
            {
                PDFOperator op = (PDFOperator) next;                   
                if (op.getOperation().equals("replace this line"))
                {
                    COSString previous = (COSString) tokens.get(j - 1);
                    String string = previous.getString();
                    string = string.replaceFirst("replace this line", "");
                    previous.reset();
                    previous.append(string.getBytes("ISO-8859-1"));
                }
            }
        }          
        PDStream updatedStream = new PDStream(doc);
        OutputStream out = updatedStream.createOutputStream();
        ContentStreamWriter tokenWriter = new ContentStreamWriter(out);
        tokenWriter.writeTokens(tokens);
        page.setContents(updatedStream);
    }
    doc.save("D://out1.pdf");