Keep object in memory after end of method [closed]

I need to load two spreadsheets to generate a dictionary with spreadsheet data.

I'm a bit confused about this .. I've created a ReadFilter method for not repeating the code, since the process is the same for both files. This method returns a dictionary with the data.

public object LerPlanilha(string range, FileInfo planilha)
{

            using (var pck = new ExcelPackage(planilha))
            {
                var worksheet = pck.Workbook.Worksheets[1];


                var cells = worksheet.Cells;
                var dictionary = cells[range]
                    .GroupBy(c => new { c.Start.Row, c.Start.Column })
                    .ToDictionary(
                        rcg => new KeyValuePair<int, int>(rcg.Key.Row, rcg.Key.Column),
                        rcg => cells[rcg.Key.Row, rcg.Key.Column].Value);

                return dictionary;
            }
}

I need to double-click on two different buttons to load the data from one worksheet at a time, in the btnModel I assign the return of LerFile in the global variable LoadedCells that is an object. I'm doing it this way

private void btnModelo_Click(object sender, EventArgs e)
        {

            var arquivo = CarregarArquivo().ToString();

            if (arquivo != "OK")
            {

                var planilhaBase = new FileInfo(arquivo);
                CelulasCarregadasModelo =  LerPlanilha("B16:AG16", planilhaBase);

                lblModeloCarregado.Visible = true;
                lblModeloNome.Visible = true;
                lblModeloCarregado.Text = "Planilha Carregada";
                lblModeloNome.Text = Path.GetFileNameWithoutExtension(arquivo);
            }

            else
            {
                lblModeloCarregado.Visible = true;
                lblModeloCarregado.Text = "Erro/Modelo não selecionado";
            }
}

And in the other button btnPlan assigns the return of LerArquivo in CellsLavagedPlan

private void btnPlan_Click(object sender, EventArgs e)
    {
                    var arquivo = CarregarArquivo().ToString();

                    if (arquivo != "OK")
                    {

                        var planilhaBase = new FileInfo(arquivo);
                        CelulasCarregadasPlan = LerPlanilha("B16:AG16", planilhaBase);

                        lblFluxoIntCarregado.Visible = true;
                        lblFluxoIntNome.Visible = true;
                        lblFluxoIntCarregado.Text = "Planilha Carregada";
                        lblFluxoIntNome.Text = Path.GetFileNameWithoutExtension(arquivo);
                    }

                    else
                    {
                        lblFluxoIntCarregado.Visible = true;
                        lblFluxoIntCarregado.Text = "Erro/Modelo não selecionado";
                    }
    }

Everything happens without problems, the variable is populated with the dictionary.

What happens is that the variables are cleaned after the end of the button method, I can not leave them loaded and then compare the two dictionaries in another method.