private void buttonFreezePanes_Click(object sender, EventArgs e) {
    //Access the active worksheet.
    Worksheet worksheet = workbook.Worksheets.ActiveWorksheet;

    // Access the cell range that is currently visible.
    CellRange visibleRange = spreadsheetControl1.VisibleRange;

    // Access the active cell. 
    Cell activeCell = spreadsheetControl1.ActiveCell;

    int rowOffset = activeCell.RowIndex - visibleRange.TopRowIndex - 1;
    int columnOffset = activeCell.ColumnIndex - visibleRange.LeftColumnIndex - 1;

    // If the active cell is outside the visible range of cells, no rows and columns are frozen.
    if (!visibleRange.IsIntersecting(activeCell)) {
        return;
    }

    if (activeCell.ColumnIndex == visibleRange.LeftColumnIndex) {
        // If the active cell matches the top left visible cell, no rows and columns are frozen.
        if (activeCell.RowIndex == visibleRange.TopRowIndex) { return; }
        else
            // Freeze visible rows above the active cell if it is located in the leftmost visible column.
            worksheet.FreezeRows(rowOffset, visibleRange);
    }

    else if (activeCell.RowIndex == visibleRange.TopRowIndex) {
        // Freeze visible columns to the left of the active cell if it is located in the topmost visible row.
        worksheet.FreezeColumns(columnOffset, visibleRange);
    }

    else {
        // Freeze both rows and columns above and to the left of the active cell.
        worksheet.FreezePanes(rowOffset, columnOffset, visibleRange);
    }
}

Private Sub buttonFreezePanes_Click(ByVal sender As Object, ByVal e As EventArgs) Handles buttonFreezePanes.Click
    'Access the active worksheet.
    Dim worksheet As Worksheet = workbook.Worksheets.ActiveWorksheet

    ' Access the cell range that is currently visible.
    Dim visibleRange As CellRange = spreadsheetControl1.VisibleRange

    ' Access the active cell.
    Dim activeCell As Cell = spreadsheetControl1.ActiveCell

    Dim rowOffset As Integer = activeCell.RowIndex - visibleRange.TopRowIndex - 1
    Dim columnOffset As Integer = activeCell.ColumnIndex - visibleRange.LeftColumnIndex - 1

    ' If the active cell is outside the visible range of cells, no rows and columns are frozen.
    If (Not visibleRange.IsIntersecting(activeCell)) Then
        Return
    End If

    If activeCell.ColumnIndex = visibleRange.LeftColumnIndex Then
        ' If the active cell matches the top left visible cell, no rows and columns are frozen.
        If activeCell.RowIndex = visibleRange.TopRowIndex Then
            Return
        Else
            ' Freeze visible rows above the active cell if it is located in the leftmost visible column.
            worksheet.FreezeRows(rowOffset, visibleRange)
        End If

    ElseIf activeCell.RowIndex = visibleRange.TopRowIndex Then
        ' Freeze visible columns to the left of the active cell if it is located in the topmost visible row.
        worksheet.FreezeColumns(columnOffset, visibleRange)

    Else
        ' Freeze both rows and columns above and to the left of the active cell.
        worksheet.FreezePanes(rowOffset, columnOffset, visibleRange)
    End If
End Sub