When you receive a signed document, and the software reports that the signature is valid, this does not mean that you can be absolutely sure that the document is the same that the sender has sent. Signing documents with software certificates is not a perfectly secure method. Numerous ways are possible to circumvent the security features. Example:
如果您收到一个签名文档，并且软件报告该签名为有效签名，这并不能保证文档就是该发件人所发送的文档。使用软件证书对文档进行签名并不是绝对安全的方法。有许多方法可以规避掉安全功能的保护。