iText 的writer.setEncryption()方法用于为生成的PDF设置密码。

private static String USER_PASSWORD = 'password';
private static String OWNER_PASSWORD = 'jack';
public static void main(String[] args) {
	try 
	{
		OutputStream file = new FileOutputStream(new File('PasswordProtected.pdf'));
		Document document = new Document();
		PdfWriter writer = PdfWriter.getInstance(document, file);
		writer.setEncryption(USER_PASSWORD.getBytes(),
				OWNER_PASSWORD.getBytes(), PdfWriter.ALLOW_PRINTING,
				PdfWriter.ENCRYPTION_AES_128);
		document.open();
		document.add(new Paragraph('为pdf设置密码'));
		document.close();
		file.close();
	} catch (Exception e) 
	{
		e.printStackTrace();
	}
}