DLI Implementation and Reference Guide - Datalogics

Digital Signatures 15.3
have signed the PDF file. This makes digital signatures useful for contracts or other
archival legal documents.
A digital signature in a PDF file has two important parts:
• the certificate
• a series of DLPDFFORM objects which form a visible indicator that a document is
signed
The certificate is supplied to DLI and contains information such as the signer's name,
their location, and a signature to validate the certificate.
Certificates are accepted in PKCS #7 format and in x.509 format. For PKCS #7
format, the calling application must be able to supply a fully-formed certificate,
complete with the signed PDF document hash (supplied by DLI); for an x.509
certificate, the hash value is calculated by DLI and supplied to the application
through a callback routine for signing. This is for security purposes; calling
applications should use secure memory routines when signing the PDF document.
The appearance of the signature is optional; if it is not set, an invisible digital
signature will be added to the PDF file created by DLI. It consists of several layers:
• a background layer
• a layer displayed before the signature is validated
• a layer for the graphical signature representation (such as a scan of a handwritten
signature or signature stamp)
• a layer containing information about the signature
Any of these layers may be omitted; if so, an empty layer is created by DLI for the
signature.