You can compare the public key with the public key that is published on the web site of the certificate authority. Whenever someone changes something in the document, this change breaks the digital signature. After the change, there will be no sign that you will see the original document.
只要有人修改文档内容，此修改就会破坏数字签名。执行修改后，将没有用以表明您所看到的是原始文档的标记。