PDF files to which a time-stamp or a digital signature is applied.
加有时间戳或数字签名的PDF文件。
The time information which is included in digital signature can replace time stamp , therefore , it leaves out the uniform time stamp server that other PKI systems have to use .
同时由于签名中所含有的时间段信息，使每个证书都自动包含时间戳，省掉时间戳服务器，节省开销。
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