I found this here http://stackoverflow.com/questions/5499562/excel-to-pdf-c-sharp-library and I love it.

ExportWorkbookToPdf.cs

public bool ExportWorkbookToPdf(string workbookPath, string outputPath)
{
    // If either required string is null or empty, stop and bail out
    if (string.IsNullOrEmpty(workbookPath) || string.IsNullOrEmpty(outputPath))
    {
        return false;
    }

    // Create COM Objects
    Microsoft.Office.Interop.Excel.Application excelApplication;
    Microsoft.Office.Interop.Excel.Workbook excelWorkbook;

    // Create new instance of Excel
    excelApplication = new Microsoft.Office.Interop.Excel.Application();

    // Make the process invisible to the user
    excelApplication.ScreenUpdating = false;

    // Make the process silent
    excelApplication.DisplayAlerts = false;

    // Open the workbook that you wish to export to PDF
    excelWorkbook = excelApplication.Workbooks.Open(workbookPath);

    // If the workbook failed to open, stop, clean up, and bail out
    if (excelWorkbook == null)
    {
        excelApplication.Quit();

        excelApplication = null;
        excelWorkbook = null;

        return false;
    }

    var exportSuccessful = true;
    try
    {
        // Call Excel's native export function (valid in Office 2007 and Office 2010, AFAIK)
        excelWorkbook.ExportAsFixedFormat(Microsoft.Office.Interop.Excel.XlFixedFormatType.xlTypePDF, outputPath);
    }
    catch (System.Exception ex)
    {
        // Mark the export as failed for the return value...
        exportSuccessful = false;

        // Do something with any exceptions here, if you wish...
        // MessageBox.Show...        
    }
    finally
    {
        // Close the workbook, quit the Excel, and clean up regardless of the results...
        excelWorkbook.Close();
        excelApplication.Quit();

        excelApplication = null;
        excelWorkbook = null;
    }

    // You can use the following method to automatically open the PDF after export if you wish
    // Make sure that the file actually exists first...
    if (System.IO.File.Exists(outputPath))
    {
        System.Diagnostics.Process.Start(outputPath);
    }

    return exportSuccessful;
}