$SearchDirectory = "C:\path\to\directory"
$Files = Get-ChildItem -Path $SearchDirectory -File
foreach($File in $Files)
{
    $FileData = Get-Content $File.FullName
    $ReplaceString = "Hello"
    $ReplaceData = "Hello+$($File.Name)"
    $NewFileData = $FileData.Replace($ReplaceString,$ReplaceData)
   
    Out-File -FilePath $File.FullName -InputObject $NewFileData -Force
}