If you want to automate the conversion from XLS to PDF, then PowerShell provides a very straight forward way to do it.  Create an Excel object, load the XLS file, write to PDF.

param(
    [Parameter(Mandatory=$true)]
    [string]$InputFileName,
    [Parameter(Mandatory=$true)]
    [string]$OutputFileName
    )

$xlFixedFormat = “Microsoft.Office.Interop.Excel.xlFixedFormatType” -as [type] 

$excel = New-Object -ComObject excel.application
$workbook = $excel.workbooks.open($InputFileName, 3)
$workbook.Saved = $true
$workbook.ExportAsFixedFormat($xlFixedFormat::xlTypePDF, $OutputFileName)
$excel.Workbooks.close()
$excel.Quit()

You then run the code with two parameters, source file, and destination file.

Source: https://blogs.technet.microsoft.com/heyscriptingguy/2010/09/06/save-a-microsoft-excel-workbook-as-a-pdf-file-by-using-powershell/