private void OnAddDocument()
        {
            Telerik.Windows.Controls.RadOpenFileDialog fileDialog = new Telerik.Windows.Controls.RadOpenFileDialog();
            fileDialog.Owner            = Application.Current.MainWindow;
            fileDialog.InitialDirectory = lastDirectory;
            fileDialog.RestoreDirectory = true;
            fileDialog.DefaultExt       = "pdf";
            fileDialog.Filter           = "pdf files (*.pdf)|*.pdf";
            bool?result = fileDialog.ShowDialog();

            if (result == null)
            {
                return;
            }
            if (result == false)
            {
                return;
            }

            // set the selected Directory as InitialDirectory for the next open
            FileInfo fileInfo = new FileInfo(fileDialog.FileName);

            lastDirectory = fileInfo.DirectoryName;

            // ReportFileName only contains filename relative to travelExpenseRoot directory
            SelectedFileName = fileDialog.FileName;

            employeeDocuments.Add(new EmployeeDocument
            {
                DateValidUntil             = null,
                DocumentContentDescription = string.Empty,
                DocumentType     = DocumentTypes.Contract,
                DocumentFileName = "",
                Employee         = selectedEmployee,
                EmployeeId       = selectedEmployee.Id
            });
            // Activate added item
            ListOfDocuments.MoveCurrentToLast();
            RaisePropertyChanged("ListOfDocuments");
            RaisePropertyChanged("SelectedDocument");
        }