When I open the signed document with Acrobat, it says that 'EldoS.SecureBlackbox' handler, used to create the signature, could not be found. What should I do?
Adobe Acrobat identifies the security handler that created the signature by its name. By default, SecureBlackbox creates signatures with 'EldoS.SecureBlackbox' name. However, you can specify any name you like using ElPDFPublicKeySecurityHandler.CustomName property.
Adobe Acrobat 'knows' two handler names:
'Adobe.PPKLite' -- the signature is validated against certificates stored in the Acrobat certificate store,
'Adobe.PPKMS' -- the signature is validated against certificates stored in system (Windows) certificate store.