Validate Method    

Check and validate the status of this signature.

 

    

Syntax		  

Truth = XSignature.Validate([Certificates])

 

    

Params		  
Name Type Description
Certificate Array each of whose items is either String or Array of Bytes An array of file paths to or data for X.509 certificate (.cer) files.
Truth Boolean Whether the signature is valid.

 

    

Notes		  
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 certificates yourself.

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 certificate files?

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 BCL).

 

    

Example		  
' Validate using certificate files
Set theDoc = Server.CreateObject("ABCpdf13.Doc")
theDoc.Read Server.MapPath("../Rez/Signed.pdf")
Dim theCerts(0)
theCerts(0) = Server.MapPath("../Rez/JohnSmith.cer")
Set theSig = theDoc.Form("Signature")
If theSig.Validate(theCerts) Then
  theDoc.AddText "Signature valid at " & Now
End If
theDoc.Save Server.MapPath("SignedAndValidated.pdf")