[PowerShell] Monitor a Folder Rename and Move New Files

I’m new to Powershell, but I’m trying to create a script that watches over a folder, and move and rename any files in that folder.

The sourcefile is 15x number and a 4 letter ending .pdf.
I need it to move and rename that file to Date+Time+Ending.pdg

So from 123456789128912ABC.pdf

to 181108_0952_ABC.pdf

This is what I have tried to do so far

$source = "C:\script\test\"
$destiantion = "c:\script\"

cd $source
$files = gci -name *.pdf
foreach ($file in $files) {
  $thename = $file.substring(20);
  $date = Get-Date -f yyMMdd
  rename-item -path $source$file -newname $thename

This scripts rename the file to ABC.pdf
But my trouble is to add date to the file.

I also want that file moved to $destination after rename.

Anyone who can assist, its probably easy for someone who know this