Rename files in Powershell with a reference file - regex

Question

Sorry for previous confusion...
I've spent several hours today trying to write a powershell script that will pull a client ID off a PDF from system #1 (example, Smith,John_H123_20171012.pdf where the client ID is the H#### value), then look it up in an Excel spreadsheet that contains the client ID in system 1 and system 2, then rename the file to the format needed for system 2 (xxx_0000000123_yyy.pdf).
One gotcha is that client # is 2-4 digits in system 2 and always preceeded by 0's.
Using Powershell and regular expressions.
This is the first part I am trying to use for my initial rename:
Get-ChildItem -Filter *.pdf | Foreach-Object{
$pattern = "_H(.*?)_2"
$OrionID = [regex]::Match($file, $pattern).Groups[1].value
Rename-Item -NewName $OrionID
}
It is not accepting "NewName" because it states it is an empty string. I have run:
Get-Variable | select name,value,Description
And new name shows up as a name but with no value. How can I pass the output from the Regex into the rename?

Answer 1

Run this code line by line in debugger, you will understand how this works.
#Starts an Excel process, you can see Excel.exe as background process
$processExcel = New-Object -com Excel.Application
#If you set it to $False you wont see whats going on on Excel App
$processExcel.visible = $True
$filePath="C:\somePath\file.xls"
#Open $filePath file
$Workbook=$processExcel.Workbooks.Open($filePath)
#Select sheet 1
$sheet = $Workbook.Worksheets.Item(1)
#Select sheet with name "Name of some sheet"
$sheetTwo = $Workbook.Worksheets.Item("Name of some sheet")
#This will store C1 text on the variable
$cellString = $sheet.cells.item(3,1).text
#This will set A4 with variable value
$sheet.cells.item(1,4) = $cellString
#Iterate through all the sheet
$lastUsedRow = $sheet.UsedRange.Rows.count
$LastUsedColumn = $sheet.UsedRange.Columns.count
for ($i = 1;$i -le $lastUsedRow; $i++){
for ($j = 1;$j -le $LastUsedColumn; $j++){
$otherString = $sheet.cells.item($i,$j).text
}
}
#Create new Workbook and add sheet to it
$newWorkBook = $processExcel.Workbooks.Add()
$newWorkBook.worksheets.add()
$newSheet = $newWorkBook.worksheets.item(1)
$newSheet.name="SomeName"
#Close the workbook, if you set $False it wont save any changes, same as close without save
$Workbook.close($True)
#$Workbook.SaveAs("C:\newPath\newFile.xls",56) #You can save as the sheet, 56 is format code, check it o internet
$newWorkBook.close($False)
#Closes Excel app
$processExcel.Quit()
#This code is to remove the Excel process from the OS, this does not always work.
[System.Runtime.Interopservices.Marshal]::ReleaseComObject($processExcel)
Remove-Variable processExcel

Answer 2

I ended up using a utility called "Bulk Rename Utility" and Excel. I can run the various renaming regex's through BRU and add the reference .txt file after some Excel formatting.