Adobe 22002486, User Manual, Page: 55 / 189

Acrobat 9 Family of Products Authoring Signable Documents
Security Feature User Guide Using Timestamps During Signing 55
1. Choose Edit > Preferences (Windows) or Acrobat > Preferences (Macintosh).
2. Choose Security in the left-hand list.
3. Highlight an appearance in the Appearance panel.
4. Choose Edit or Delete .
5. Edit the appearance. For details, see “Creating a Custom Signature Appearance” on page 53 .
6. Choose OK .
4.2.3 Using Timestamps During Signing
Signature times tell you that a document and signature existed prior to the indicated time. All signatures
are associated with the signer machine’s local time, but they may also include a timestamp time provided
by a timestamp server if one is configured. Because a user can set that time forward or back, a local time is
less reliable than a timestamp time. Local times are labelled as such in the Date/Time and Summary tabs of
the Signature Property dialog (
Figure 43 ).
Note: Because signature appearances only display local time, the appearance time will be
different from the timestamp time shown in the Date/Time tab of the Signature
Properties dialog.
Figure 43 Timestamps: Local, machine time
Like signatures, timestamps are provided by someone (a timestamp authority) who uses certificates to
confirm their identity. Before you can validate a timestamp, you must explicitly trust the timestamp
authority’s certificate. Timestamp certificate status appears in the Date/Time and Summary tabs of the
Signature Property dialog:

Untrusted timestamp certificates appear as follows:
Figure 44 Timestamps: Untrusted stamp

Trusted timestamps that have been added to the Trusted Identities list and have been explicitly trusted
for signing appear as follows:
Figure 45 Timestamps: Trusted stamp
Timestamps are usually provided by third-party timestamp authorities such as GeoTrust. Because
timestamp authorities may charge for their services, Acrobat does not automatically set a default
timestamp server if multiple servers are listed. Users must manually specify which timestamp server to use
as the default.