|This method returns true if the signature is valid. To be
precise, this method updates the properties IsModified, IsTimeValid and IsTrusted. The return value is true only if the IsModified is false, and both IsTimeValid and
IsTrusted are true.
Signatures' certificates can only be validated by referencing
certificates issued by certification authorities.
This method allows you to check and validate the status of a
signature with reference to a set of such certificates.
Additionally, ABCpdf can also use certificates found in the Windows
Certificate Store for validation. See ValidationPolicy for details.
The certificates you provide will be cached at a document level
so this method is efficient even when checking multiple signatures
within one document. If you do not provide any parameter, this
method will use the previously cached certificates to validate the
document. Therefore, unless ValidationPolicy is set
to EntireChainTrust, or certificates have been provided using a
previous call to this method, calling this method without any
certificate will cause an error to be raised to indicate that there
is no certificate to validate against.
ABCpdf does not currently do revocation checks on certificates
provided and on certificates embedded in a PDF document. If you
need to do this type of operation, you should use the GetCertificates method and check the
If a certificate is unavailable or invalid, this method may
raise an error. This means validating against an unsigned signature
field will cause an error to be raised.
How does Adobe Reader validate a PDF document without
You may find that Adobe Reader does not need a list of
certificate files to validate PDF documents. This is because Adobe
Reader may use several built-in Public Key Infrastructure
hierarchies to certify PDF documents:
- Certified Document Services (CDS) is a trust
hierarchy that chains back to the Adobe Root Certification
Authority (Adobe Root CA).
- Adobe Approved Trust List (AATL) is an extra
list of CA certificates that Adobe Reader may download from Adobe
periodically (for Adobe Reader/Acrobat 9 or later).
- The Windows Certificate Store. This is only true if Windows
digital signature integration is enabled in Acrobat, which is not
the default for Acrobat 9 and X.
In order to validate a PDF document the same way Adobe Reader
does, you need to use the same certificates it uses. This can be
easily achieved by exporting the trusted identities from
Adobe Reader to .cer format certificate files. (Note: CDS and AATL
certificates are usually not in your Windows Certificate
Store by default.)
The Windows Certificate Store can be accessed by using
System.Security.Cryptography.X509Certificates.X509Store (in .NET