When I use Apache-POI to convert PPTX to PDF on Android, it reports 'java.lang.RuntimeException: Couldn't open the font file'. The code is as follows:``` public static boolean convertPPTToPDF(File file, File toFile) {
try {
Document pdfDocument = new Document();
PdfWriter pdfWriter = PdfWriter.getInstance(pdfDocument, new FileOutputStream(toFile));
FileInputStream is = new FileInputStream(file);
double zoom = 2;
is = new FileInputStream(file);
XMLSlideShow ppt = convertPPTToPDFByPPTX(is);
if (ppt == null) {
throw new NullPointerException("This PPTX get data is error....");
}
Dimension pgsize = ppt.getPageSize();
List<XSLFSlide> slide = Arrays.asList(ppt.getSlides());
AffineTransform at = new AffineTransform();
at.setToScale(zoom, zoom);
pdfDocument.setPageSize(new com.lowagie.text.Rectangle((float) pgsize.getWidth(), (float) pgsize.getHeight()));
pdfWriter.open();
pdfDocument.open();
PdfPTable table = new PdfPTable(1);
for (XSLFSlide xslfSlide : slide) {
BufferedImage img = new BufferedImage((int) Math.ceil(pgsize.width * zoom), (int) Math.ceil(pgsize.height * zoom), BufferedImage.TYPE_INT_RGB);
/*InputStream open = AppManager.getAppManager().getTopActivity().getAssets().open("fonts/simsun.ttf");
java.awt.Font fonts = java.awt.Font.createFont(java.awt.Font.TRUETYPE_FONT, open);
java.awt.GraphicsEnvironment localGraphicsEnvironment = java.awt.GraphicsEnvironment.getLocalGraphicsEnvironment();*/
Graphics2D graphics = img.createGraphics();
graphics.setTransform(at);
graphics.setPaint(Color.white);
graphics.fill(new Rectangle2D.Float(0, 0, pgsize.width, pgsize.height));
xslfSlide.draw(graphics);
graphics.getPaint();
com.lowagie.text.Image slideImage = com.lowagie.text.Image.getInstance(img, null);
table.addCell(new PdfPCell(slideImage, true));
}