我尝试为我的pdf生成一个toc（目录），并且我想使用ITextExtractionStrategy获得一些类似于xxx.pdf中章节标题的字符串。但是运行测试时出现了com.itextpdf.kernel.PdfException。

这是我的代码：

    @org.junit.Test
    public void test() throws IOException {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        PdfDocument pdfDoc = new PdfDocument(new PdfReader("src/test/resources/template/xxx.pdf"),
                new PdfWriter(baos));

        pdfDoc.addNewPage(1);
        Document document = new Document(pdfDoc);

        // when add this code, throw com.itextpdf.kernel.PdfException: Dictionary doesn't have supported font data.
        Paragraph title =  new Paragraph(new Text("index"))
                .setTextAlignment(TextAlignment.CENTER);
        document.add(title);

        SimpleTextExtractionStrategy extractionStrategy = new SimpleTextExtractionStrategy();
        for (int i = 1; i < pdfDoc.getNumberOfPages(); i++) {
            PdfPage page = pdfDoc.getPage(i);
            PdfCanvasProcessor parser = new PdfCanvasProcessor(extractionStrategy);
            parser.processPageContent(page);
        }
        ...

        document.close();
        pdfDoc.close();
        new FileOutputStream("./yyy.pdf").write(baos.toByteArray());
    }

这是输出：

com.itextpdf.kernel.PdfException: Dictionary doesn't have supported font data.

    at com.itextpdf.kernel.font.PdfFontFactory.createFont(PdfFontFactory.java:123)
    at com.itextpdf.kernel.pdf.canvas.parser.PdfCanvasProcessor.getFont(PdfCanvasProcessor.java:490)
    at com.itextpdf.kernel.pdf.canvas.parser.PdfCanvasProcessor$SetTextFontOperator.invoke(PdfCanvasProcessor.java:811)
    at com.itextpdf.kernel.pdf.canvas.parser.PdfCanvasProcessor.invokeOperator(PdfCanvasProcessor.java:454)
    at com.itextpdf.kernel.pdf.canvas.parser.PdfCanvasProcessor.processContent(PdfCanvasProcessor.java:282)
    at com.itextpdf.kernel.pdf.canvas.parser.PdfCanvasProcessor.processPageContent(PdfCanvasProcessor.java:303)
    at com.example.pdf.util.Test.test(Test.java:138)