Use the timestamp for signing

Timestamping is used mainly to ensure the time, at which the action is performed. In digital security world, this means fixing the time, at which the document is signed.

Various digital signature standards include (or don't include) their own timestamping procedures.

MS Authenticode supports timestamping by including a timestamp as a countersignature to PE file (see the corresponding how-to article).

PKCS#7 supports timestamping by including a timestamp as an unauthenticated attribute (see the corresponding how-to article)

PDF supports timestamping as a part of file format (see the corresponding how-to article)

XMLDSig doesn't specify the timestamping procedures. Each implementation adds it's own procedures for this. The attempt to standardize the timestamping was made in XAdES-T standard, which is a superset of XMLDSig.