Example that can, a) download a secure document and b) convert an excel to csv using local client application

Convert-Online-Excel-To-Local-CSV.ps1

#summary
#this script downloads an Excel document, saves it locally, and converts it to CSV
#by tiago duarte @ 15-sep-2015
#http://about.me/tiagoduarte

#set parameters for calling externally
param(
	
	$xlsUrl = "http://mywebsite.com/mydocument.xlsx",	
	$tempName = "downloaded-spreadsheet",	
	$tempPath = "c:\temp\$tempName.xlsx"
)

#http://stackoverflow.com/questions/508565/how-to-make-an-authenticated-web-request-in-powershell
function DownloadFile($source, $destination)
{	
	if(test-path $destination)
	{
		write-host ("Removing previously downloaded file..." + $nl)
		rm $destination
	}
	
	write-host ("Downloading $source..." + $nl)
	
	$wc = New-Object System.Net.WebClient
	$wc.Credentials = $credentials
	$wc.DownloadFile($source, $destination)
	$wc.Dispose()
}

#http://stackoverflow.com/questions/27293481/convert-multiple-xls-to-csv-using-powershell
function ConvertExcel-ToCSV($source)
{
	$excelVisible = $false
	$excelCompatCheck = $false
	$excelSaveChanges = $false

	$file = gci $source
	$newname = $file.FullName -replace '\.xlsx$', '.csv'
	
	if(test-path $newname)
	{
		write-host ("Removing previous csv..." + $nl)
		rm $newname
	}
	
	write-host ("Converting $source to CSV..." + $nl)
	
	$ExcelWB = new-object -comobject excel.application -Property @{Visible = $excelVisible} 
	$Workbook = $ExcelWB.Workbooks.Open($file.FullName)
	$Workbook.CheckCompatibility = $excelCompatCheck
	$Workbook.SaveAs($newname, 6)
	$Workbook.Close($excelSaveChanges)
	$ExcelWB.Quit()
	#this line is crucial in order to effectively close the Excel process started by the command line
	[Runtime.Interopservices.Marshal]::ReleaseComObject($ExcelWB) | Out-Null
	
	$Workbook = $null
	$ExcelWB = $null
	
	if(test-path $source)
	{
		rm $source
		write-host ("Removing source file..." + $nl)
	}	
}

try
{
	clear-host
	
	$global:nl = [Environment]::NewLine	
	
	$user = read-host "Username"
	$pass = read-host -assecurestring "Password"
	$domain = read-host "Domain"
	$global:credentials = new-object System.Net.NetworkCredential($user, $pass, $domain)
	
	#$global:credentials = new-object System.Net.NetworkCredential("testuser", "pass", "domain")
	
	write-host ("Script execution started!" + $nl)
	
	DownloadFile $xlsUrl $tempPath
	
	ConvertExcel-ToCSV $tempPath
	
	#Get-Process | Where-Object {$_.Path -like "*Excel.exe*"} | Stop-Process	
}
catch
{
	write-host ($nl)
	write-warning "Program Crashed!"
	write-host ($nl)
	$_.Exception
	write-host ($nl)
	write-host ("ScriptName: " + ($_.InvocationInfo.ScriptName.Substring($_.InvocationInfo.ScriptName.lastIndexOf("\")+1)) + $nl)
	write-host ("Line:       " + $_.InvocationInfo.ScriptLineNumber + $nl)# + " - Column: " + $_.InvocationInfo.OffsetInLine + $nl)
    write-host ("Column:     " + $_.InvocationInfo.OffsetInLine + $nl)
	write-host ("Type:       " + $_.CategoryInfo.Reason + $nl)
}
finally
{
	write-host ("Script execution ended!" + $nl)
}