下面是方法，直接調用
public static void sign(String beforePdfpath,String afterPdfpath,String pngpath) throws Exception {
// KeyStore ks = KeyStore.getInstance("pkcs12");
// ks.load(new FileInputStream("demo.p12"),"123456".toCharArray()); //123456為私鑰密碼
// String alias = (String) ks.aliases().nextElement();
// PrivateKey key = (PrivateKey) ks.getKey(alias, "123456".toCharArray());
// Certificate[] chain = ks.getCertificateChain(alias);
Log.d("pdfd", "do-1");
PdfReader reader = new PdfReader(beforePdfpath); //源文件
Log.d("pdfd", "do-1-01");
FileOutputStream fout = new FileOutputStream(afterPdfpath);
Log.d("pdfd", "do-1-1");
PdfStamper stp = PdfStamper.createSignature(reader, fout, '\0');
PdfSignatureAppearance sap = stp.getSignatureAppearance();
// sap.setCrypto(key, chain, null, PdfSignatureAppearance.VERISIGN_SIGNED);
Log.d("pdfd", "do-2");
sap.setReason("");
sap.setLocation("");
sap.setContact("/");
Image image = Image.getInstance(pngpath); //使用png格式透明圖片
Log.d("pdfd", "do-3");
sap.setSignatureGraphic(image);
sap.setAcro6Layers(true);
sap.setRenderingMode(RenderingMode.GRAPHIC);
sap.setVisibleSignature(new Rectangle(300, 600, 400, 675), 1, null); //300和600 是對應x軸和y軸坐標
stp.getWriter().setCompressionLevel(5);
Log.d("pdfd", "do-4");
if (stp != null) {
Log.d("pdfd", "do-4-1");
stp.close();
Log.d("pdfd", "do-4-2");
}
Log.d("pdfd", "do-5");
if (fout != null) {
fout.close();
}
Log.d("pdfd", "do-6");
if (reader != null) {
reader.close();
}
Log.d("pdfd", "do-7");
}