android - Androidでhtmlをpdfに変換する

Question

HTMLファイルをPDFに変換したい私のコードは

Document document = new Document();
boolean mExternalStorageAvailable = false;
boolean mExternalStorageWriteable = false;
String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state)) {
    mExternalStorageAvailable = mExternalStorageWriteable = true;
} else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
    mExternalStorageAvailable = true;
    mExternalStorageWriteable = false;
} else {
    mExternalStorageAvailable = mExternalStorageWriteable = false;
}
String file = null;
if (mExternalStorageWriteable) {
    file = Environment.getExternalStorageDirectory() + "/abcd.pdf";
}

document.open();
PdfCopy writer = new PdfCopy(document, new FileOutputStream(file));

InputStream is = new FileInputStream(Environment.getExternalStorageDirectory()+"/new1.html");

PdfReader reader = new PdfReader(is);

PdfImportedPage page;
int n = reader.getNumberOfPages();
page = writer.getImportedPage(reader, n);
Image instance = Image.getInstance(page);
document.add(instance);

document.close();
Toast.makeText(this, "pdf created", Toast.LENGTH_LONG).show();

itextpdf-5.4.3.jar を使用しました。このコードを実行しているときに、「PDF ヘッダー署名が見つかりません」という例外が発生します...誰か助けてくれますか