Code snippet to get the most recent .bak file

Copy-LastSQLBackup.ps1

#raw example
$sourcepath = 'C:\DBBackups\AdventureWorks2012'
$targetpath = 'C:\DBBackups\Archive'

#You can use 'dir' instead of Get-ChildItem
Get-ChildItem $sourcepath *.bak | Sort-Object LastWriteTime -Descending | Select-Object -First 1 | Copy-Item -Destination $targetpath

#function
function Copy-LastSQLBackup{
    param([string]$sourcepath
         ,[string]$targetpath)

    Get-ChildItem $sourcepath *.bak | Sort-Object LastWriteTime -Descending | Select-Object -First 1 | Copy-Item -Destination  $targetpath
}

#Example
Copy-LastSQLBackup -sourcepath C:\DBBackups\AdventureWorks2012SMO -targetpath C:\DBBackups\Archive