Sample flow

$files = Get-ChildItem -File | Where-Object { $_.Name -match "PARS_Rpt110_" }

foreach ($file in $files) {

    $baseName = $file.Name.Substring($file.Name.IndexOf("PARS_Rpt110_"))

    $newName = $baseName

    $counter = 1

    while (Test-Path -LiteralPath (Join-Path $file.DirectoryName $newName)) {

        $nameOnly = [System.IO.Path]::GetFileNameWithoutExtension($baseName)

        $ext = $file.Extension

        $newName = "$nameOnly ($counter)$ext"

        $counter++

    }

    Rename-Item -Path $file.FullName -NewName $newName

}