pdf-util

PDF签名工具，将一张png图片覆盖到PDF文件上面，类似这样：

依赖

<dependency>
  <groupId>com.github.dreamroute</groupId>
  <artifactId>pdf-util</artifactId>
  <version>最新-RELEASE</version>
</dependency>

调用SignUtil.sign方法即可