RadGridview 1.BestFitColumns(Telerik.WinControls.UI.BestFitColumnMode.HeaderCells)

DataTable table = new DataTable();
for (int i = 0; i < 20; i++)
{
    table.Columns.Add("Left" + i, typeof(int));
    table.Columns.Add("Right" + i, typeof(int));
}

for (int i = 0; i < 27; i++)
{
    List<object> parameters = new List<object>();
    for (int j = 0; j < table.Columns.Count - 2; j++)
    {
        parameters.Add(100 * i + i);
    }

    table.Rows.Add(parameters.ToArray());
}

this.radGridView1.DataSource = table;

ColumnGroupsViewDefinition def = new ColumnGroupsViewDefinition();
for (int i = 0, j = 0; i < 20; i++)
{
    var group = new GridViewColumnGroup("Group" + 3 + i);
    def.ColumnGroups.Add(group);
    group.Groups.Add(new GridViewColumnGroup("0"));
    group.Groups[0].Rows.Add(new GridViewColumnGroupRow() { MinHeight = 30});
    group.Groups[0].Rows[0].ColumnNames.Add(this.radGridView1.Columns[j].Name);
    this.radGridView1.Columns[j].Width = 58;
    j++;
    group.Groups[0].Rows[0].ColumnNames.Add(this.radGridView1.Columns[j].Name);
    this.radGridView1.Columns[j].Width = 58;
    j++;
}

radGridView1.MasterTemplate.ShowRowHeaderColumn = false;
this.radGridView1.ViewDefinition = def;

// To Export:
GridViewPdfExport pdfExport = new GridViewPdfExport(this.radGridView1);
pdfExport.FitToPageWidth = false;
pdfExport.ExportViewDefinition = true;
pdfExport.ExportVisualSettings = true;
pdfExport.RunExport(@"..\..\pdf", new PdfExportRenderer());