This function returns true if the signature is valid.
To be precise, this method updates the properties Algorithm, IsModified, IsTimeValid, IsTrusted and CompliancePades. The
return value is true only if the IsModified is
false, and all of IsTimeValid, IsSecure and IsTrusted are true.
While the SigningRevision does not
affect validity you should be careful to take it into account when
reporting back to the user. Similarly there are some subtleties
relating to the IsTrusted property which are
worth bearing in mind.
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 function is efficient even when checking multiple
signatures within one document. If you do not provide any
parameters, this function 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 function, calling
the parameterless version of this function will cause an exception
to be thrown to indicate that there are no certificates to validate
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 function and check the
If a certificate is unavailable or invalid, this method may
throw an exception. This means validating against an unsigned
signature field will cause an exception to be thrown.
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 has not
been the default since Acrobat 9.
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.).
These then need to be placed in the Windows Certificate Store.
For them to be trusted they need to be in one of the Trusted folder
- Trusted People or Trusted Root Certification Authorities.
Needless to say, adding items to these folders - particularly the
latter - is a big deal and you must be very careful to ensure you
know what you are doing.
The Windows Certificate Store can be accessed by using