//Поиск сертификата по серийному номеру
function getSignerCertificate(SerialNumber: string): Variant;
const
  CAPICOM_CURRENT_USER_STORE = 2;
var
  oStore: Variant;
  i: integer;
begin
  result := Unassigned;
  oStore := CreateOLEObject('CAdESCOM.Store');
  oStore.Open(CAPICOM_CURRENT_USER_STORE);
  for i := 1 to oStore.Certificates.Count - 1 do
    if oStore.Certificates.Item[i].SerialNumber = SerialNumber then
    begin
      result := oStore.Certificates.Item[i];
      Exit;
    end;
end;

//Подпись по отпечатку
function GetCertificateOfStamp(thumbprint: string; var oCertificate: olevariant; var onErr: string): boolean;
const
  CAPICOM_MY_STORE = 'MY';
  CAPICOM_CERTIFICATE_FIND_SHA1_HASH = $00000000;
  CAPICOM_CURRENT_USER_STORE = 2;
  CAPICOM_STORE_OPEN_MAXIMUM_ALLOWED = 2;
var
  oStore, oCertificates: olevariant;
  x: integer;
begin
  onErr := '';
  result := false;
  try
    oStore := CreateOleObject('CAdESCOM.Store');
    oStore.Open(CAPICOM_CURRENT_USER_STORE, CAPICOM_MY_STORE, CAPICOM_STORE_OPEN_MAXIMUM_ALLOWED);

    oCertificates := oStore.Certificates.Find(CAPICOM_CERTIFICATE_FIND_SHA1_HASH, widestring(thumbprint));

    x := oCertificates.Count;
    if x = 0 then
    begin
      onErr := 'Не найден сертификат с отпечатком: [' + thumbprint + ']';
      exit;
    end;
    oCertificate := oCertificates.Item[1]; // oCertificates.Item(1);
    result := true;
  except
    on e: exception do
    begin
      onErr := 'Не удалось получить доступ к сертификату с отпечатком: [' + thumbprint + '] ' + e.Message;
    end;
  end;
end;