[Serializable]
public class DocItem 
{
    public string path;
    public string code;
    public OperType type;
}

   
            DocItem item = new DocItem();
            List<DocItem> docList = new List<DocItem>();
...........
            AppDomain appDomain = null;
            AppDomainSetup appDomainSetup = new AppDomainSetup();
            appDomainSetup.ShadowCopyFiles = "false";
            appDomainSetup.ApplicationBase = AppDomain.CurrentDomain.BaseDirectory;
            appDomainSetup.PrivateBinPath = Constants.pathToBin;
            appDomain = AppDomain.CreateDomain("new domain", AppDomain.CurrentDomain.Evidence, appDomainSetup);

            Worker worker = (Worker)appDomain.CreateInstanceFromAndUnwrap(
                      typeof(Worker).Assembly.Location, typeof(Worker).FullName);

            worker.PrintByItem(item); //1
            или            
            worker.PrintByList(docList); //2

Worker.DocItem item = new Worker.DocItem();
List<Worker.DocItem> itemList = new List<Worker.DocItem>();
foreach (int i in lbRegName.GetSelectedIndices()) {
    item.path = Constants.pathToReports + getReportByValue(lbRegName.Items[i].Value);                   
    item.code = lbRegName.Items[i].Value.ToString();
    itemList.Add(item);
}
if (list != null) {
using (MemoryStream stream = new MemoryStream()){
    BinaryFormatter bin = new BinaryFormatter();
    bin.Context = new StreamingContext(StreamingContextStates.Clone);
    bin.Serialize(stream, itemList);
    worker.PrintByList(stream);
}      

public void PrintByList(MemoryStream itemList) {
  List<DocItem> item = new List<DocItem>();
  BinaryFormatter bin = new BinaryFormatter();
  bin.Context = new StreamingContext( StreamingContextStates.Clone );
  itemList.Position = 0;
  item = (List<DocItem>)bin.Deserialize(itemList); <-- exception here
}